feat(#82): implement Personality Module

- Add Personality model to Prisma schema with FormalityLevel enum
- Create migration and seed with 6 default personalities
- Implement CRUD API with TDD approach (97.67% coverage)
  * PersonalitiesService: findAll, findOne, findDefault, create, update, remove
  * PersonalitiesController: REST endpoints with auth guards
  * Comprehensive test coverage (21 passing tests)
- Add Personality types to shared package
- Create frontend components:
  * PersonalitySelector: dropdown for choosing personality
  * PersonalityPreview: preview personality style and system prompt
  * PersonalityForm: create/edit personalities with validation
  * Settings page: manage personalities with CRUD operations
- Integrate with Ollama API:
  * Support personalityId in chat endpoint
  * Auto-inject system prompt from personality
  * Fall back to default personality if not specified
- API client for frontend personality management

All tests passing with 97.67% backend coverage (exceeds 85% requirement)

apps/api/src/common/utils/index.ts

@@ -0,0 +1 @@
+export * from "./query-builder";

apps/api/src/common/utils/query-builder.spec.ts

@@ -0,0 +1,183 @@
+import { describe, expect, it } from "vitest";
+import { QueryBuilder } from "./query-builder";
+import { SortOrder } from "../dto";
+
+describe("QueryBuilder", () => {
+  describe("buildSearchFilter", () => {
+    it("should return empty object when search is undefined", () => {
+      const result = QueryBuilder.buildSearchFilter(undefined, ["title", "description"]);
+      expect(result).toEqual({});
+    });
+
+    it("should return empty object when search is empty string", () => {
+      const result = QueryBuilder.buildSearchFilter("", ["title", "description"]);
+      expect(result).toEqual({});
+    });
+
+    it("should build OR filter for multiple fields", () => {
+      const result = QueryBuilder.buildSearchFilter("test", ["title", "description"]);
+      expect(result).toEqual({
+        OR: [
+          { title: { contains: "test", mode: "insensitive" } },
+          { description: { contains: "test", mode: "insensitive" } },
+        ],
+      });
+    });
+
+    it("should handle single field", () => {
+      const result = QueryBuilder.buildSearchFilter("test", ["title"]);
+      expect(result).toEqual({
+        OR: [
+          { title: { contains: "test", mode: "insensitive" } },
+        ],
+      });
+    });
+
+    it("should trim search query", () => {
+      const result = QueryBuilder.buildSearchFilter("  test  ", ["title"]);
+      expect(result).toEqual({
+        OR: [
+          { title: { contains: "test", mode: "insensitive" } },
+        ],
+      });
+    });
+  });
+
+  describe("buildSortOrder", () => {
+    it("should return default sort when sortBy is undefined", () => {
+      const result = QueryBuilder.buildSortOrder(undefined, undefined, { createdAt: "desc" });
+      expect(result).toEqual({ createdAt: "desc" });
+    });
+
+    it("should build single field sort", () => {
+      const result = QueryBuilder.buildSortOrder("title", SortOrder.ASC);
+      expect(result).toEqual({ title: "asc" });
+    });
+
+    it("should build multi-field sort", () => {
+      const result = QueryBuilder.buildSortOrder("priority,dueDate", SortOrder.DESC);
+      expect(result).toEqual([
+        { priority: "desc" },
+        { dueDate: "desc" },
+      ]);
+    });
+
+    it("should handle mixed sorting with custom order per field", () => {
+      const result = QueryBuilder.buildSortOrder("priority:asc,dueDate:desc");
+      expect(result).toEqual([
+        { priority: "asc" },
+        { dueDate: "desc" },
+      ]);
+    });
+
+    it("should use default order when not specified per field", () => {
+      const result = QueryBuilder.buildSortOrder("priority,dueDate", SortOrder.ASC);
+      expect(result).toEqual([
+        { priority: "asc" },
+        { dueDate: "asc" },
+      ]);
+    });
+  });
+
+  describe("buildDateRangeFilter", () => {
+    it("should return empty object when both dates are undefined", () => {
+      const result = QueryBuilder.buildDateRangeFilter("createdAt", undefined, undefined);
+      expect(result).toEqual({});
+    });
+
+    it("should build gte filter when only from date is provided", () => {
+      const date = new Date("2024-01-01");
+      const result = QueryBuilder.buildDateRangeFilter("createdAt", date, undefined);
+      expect(result).toEqual({
+        createdAt: { gte: date },
+      });
+    });
+
+    it("should build lte filter when only to date is provided", () => {
+      const date = new Date("2024-12-31");
+      const result = QueryBuilder.buildDateRangeFilter("createdAt", undefined, date);
+      expect(result).toEqual({
+        createdAt: { lte: date },
+      });
+    });
+
+    it("should build both gte and lte filters when both dates provided", () => {
+      const fromDate = new Date("2024-01-01");
+      const toDate = new Date("2024-12-31");
+      const result = QueryBuilder.buildDateRangeFilter("createdAt", fromDate, toDate);
+      expect(result).toEqual({
+        createdAt: {
+          gte: fromDate,
+          lte: toDate,
+        },
+      });
+    });
+  });
+
+  describe("buildInFilter", () => {
+    it("should return empty object when values is undefined", () => {
+      const result = QueryBuilder.buildInFilter("status", undefined);
+      expect(result).toEqual({});
+    });
+
+    it("should return empty object when values is empty array", () => {
+      const result = QueryBuilder.buildInFilter("status", []);
+      expect(result).toEqual({});
+    });
+
+    it("should build in filter for single value", () => {
+      const result = QueryBuilder.buildInFilter("status", ["ACTIVE"]);
+      expect(result).toEqual({
+        status: { in: ["ACTIVE"] },
+      });
+    });
+
+    it("should build in filter for multiple values", () => {
+      const result = QueryBuilder.buildInFilter("status", ["ACTIVE", "PENDING"]);
+      expect(result).toEqual({
+        status: { in: ["ACTIVE", "PENDING"] },
+      });
+    });
+
+    it("should handle single value as string", () => {
+      const result = QueryBuilder.buildInFilter("status", "ACTIVE" as any);
+      expect(result).toEqual({
+        status: { in: ["ACTIVE"] },
+      });
+    });
+  });
+
+  describe("buildPaginationParams", () => {
+    it("should use default values when not provided", () => {
+      const result = QueryBuilder.buildPaginationParams(undefined, undefined);
+      expect(result).toEqual({
+        skip: 0,
+        take: 50,
+      });
+    });
+
+    it("should calculate skip based on page and limit", () => {
+      const result = QueryBuilder.buildPaginationParams(2, 20);
+      expect(result).toEqual({
+        skip: 20,
+        take: 20,
+      });
+    });
+
+    it("should handle page 1", () => {
+      const result = QueryBuilder.buildPaginationParams(1, 25);
+      expect(result).toEqual({
+        skip: 0,
+        take: 25,
+      });
+    });
+
+    it("should handle large page numbers", () => {
+      const result = QueryBuilder.buildPaginationParams(10, 50);
+      expect(result).toEqual({
+        skip: 450,
+        take: 50,
+      });
+    });
+  });
+});

apps/api/src/common/utils/query-builder.ts

@@ -0,0 +1,175 @@
+import { SortOrder } from "../dto";
+
+/**
+ * Utility class for building Prisma query filters
+ * Provides reusable methods for common query operations
+ */
+export class QueryBuilder {
+  /**
+   * Build a full-text search filter across multiple fields
+   * @param search - Search query string
+   * @param fields - Fields to search in
+   * @returns Prisma where clause with OR conditions
+   */
+  static buildSearchFilter(
+    search: string | undefined,
+    fields: string[]
+  ): Record<string, any> {
+    if (!search || search.trim() === "") {
+      return {};
+    }
+
+    const trimmedSearch = search.trim();
+
+    return {
+      OR: fields.map((field) => ({
+        [field]: {
+          contains: trimmedSearch,
+          mode: "insensitive" as const,
+        },
+      })),
+    };
+  }
+
+  /**
+   * Build sort order configuration
+   * Supports single or multi-field sorting with custom order per field
+   * @param sortBy - Field(s) to sort by (comma-separated)
+   * @param sortOrder - Default sort order
+   * @param defaultSort - Fallback sort order if sortBy is undefined
+   * @returns Prisma orderBy clause
+   */
+  static buildSortOrder(
+    sortBy?: string,
+    sortOrder?: SortOrder,
+    defaultSort?: Record<string, string>
+  ): Record<string, string> | Record<string, string>[] {
+    if (!sortBy) {
+      return defaultSort || { createdAt: "desc" };
+    }
+
+    const fields = sortBy.split(",").map((f) => f.trim());
+
+    if (fields.length === 1) {
+      // Check if field has custom order (e.g., "priority:asc")
+      const [field, customOrder] = fields[0].split(":");
+      return {
+        [field]: customOrder || sortOrder || SortOrder.DESC,
+      };
+    }
+
+    // Multi-field sorting
+    return fields.map((field) => {
+      const [fieldName, customOrder] = field.split(":");
+      return {
+        [fieldName]: customOrder || sortOrder || SortOrder.DESC,
+      };
+    });
+  }
+
+  /**
+   * Build date range filter
+   * @param field - Date field name
+   * @param from - Start date
+   * @param to - End date
+   * @returns Prisma where clause with date range
+   */
+  static buildDateRangeFilter(
+    field: string,
+    from?: Date,
+    to?: Date
+  ): Record<string, any> {
+    if (!from && !to) {
+      return {};
+    }
+
+    const filter: Record<string, any> = {};
+
+    if (from || to) {
+      filter[field] = {};
+      if (from) {
+        filter[field].gte = from;
+      }
+      if (to) {
+        filter[field].lte = to;
+      }
+    }
+
+    return filter;
+  }
+
+  /**
+   * Build IN filter for multi-select fields
+   * @param field - Field name
+   * @param values - Array of values or single value
+   * @returns Prisma where clause with IN condition
+   */
+  static buildInFilter<T>(
+    field: string,
+    values?: T | T[]
+  ): Record<string, any> {
+    if (!values) {
+      return {};
+    }
+
+    const valueArray = Array.isArray(values) ? values : [values];
+
+    if (valueArray.length === 0) {
+      return {};
+    }
+
+    return {
+      [field]: { in: valueArray },
+    };
+  }
+
+  /**
+   * Build pagination parameters
+   * @param page - Page number (1-indexed)
+   * @param limit - Items per page
+   * @returns Prisma skip and take parameters
+   */
+  static buildPaginationParams(
+    page?: number,
+    limit?: number
+  ): { skip: number; take: number } {
+    const actualPage = page || 1;
+    const actualLimit = limit || 50;
+
+    return {
+      skip: (actualPage - 1) * actualLimit,
+      take: actualLimit,
+    };
+  }
+
+  /**
+   * Build pagination metadata
+   * @param total - Total count of items
+   * @param page - Current page
+   * @param limit - Items per page
+   * @returns Pagination metadata object
+   */
+  static buildPaginationMeta(
+    total: number,
+    page: number,
+    limit: number
+  ): {
+    total: number;
+    page: number;
+    limit: number;
+    totalPages: number;
+    hasNextPage: boolean;
+    hasPrevPage: boolean;
+  } {
+    const totalPages = Math.ceil(total / limit);
+
+    return {
+      total,
+      page,
+      limit,
+      totalPages,
+      hasNextPage: page < totalPages,
+      hasPrevPage: page > 1,
+    };
+  }
+}