feat(knowledge): add tag management API (KNOW-003)

- Add Tag DTOs (CreateTagDto, UpdateTagDto) with validation
- Implement TagsService with CRUD operations
- Add TagsController with authenticated endpoints
- Support automatic slug generation from tag names
- Add workspace isolation for tags
- Include entry count in tag responses
- Add findOrCreateTags method for entry creation/update
- Implement comprehensive test coverage (29 tests passing)

Endpoints:
- GET /api/knowledge/tags - List workspace tags
- POST /api/knowledge/tags - Create tag
- GET /api/knowledge/tags/:slug - Get tag by slug
- PUT /api/knowledge/tags/:slug - Update tag
- DELETE /api/knowledge/tags/:slug - Delete tag
- GET /api/knowledge/tags/:slug/entries - List entries with tag

Related: KNOW-003

apps/api/src/knowledge/dto/entry-query.dto.ts

@@ -0,0 +1,29 @@
+import { IsOptional, IsEnum, IsString, IsInt, Min, Max } from "class-validator";
+import { Type } from "class-transformer";
+import { EntryStatus } from "@prisma/client";
+
+/**
+ * DTO for querying knowledge entries (list endpoint)
+ */
+export class EntryQueryDto {
+  @IsOptional()
+  @IsEnum(EntryStatus, { message: "status must be a valid EntryStatus" })
+  status?: EntryStatus;
+
+  @IsOptional()
+  @IsString({ message: "tag must be a string" })
+  tag?: string;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt({ message: "page must be an integer" })
+  @Min(1, { message: "page must be at least 1" })
+  page?: number;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt({ message: "limit must be an integer" })
+  @Min(1, { message: "limit must be at least 1" })
+  @Max(100, { message: "limit must not exceed 100" })
+  limit?: number;
+}