feat(#129): add LLM provider admin API endpoints

Implement REST API endpoints for managing LLM provider instances.

Changes:
- Created DTOs for provider CRUD operations (CreateLlmProviderDto, UpdateLlmProviderDto, LlmProviderResponseDto)
- Implemented LlmProviderAdminController with full CRUD endpoints:
  - GET /llm/admin/providers - List all providers
  - GET /llm/admin/providers/:id - Get provider details
  - POST /llm/admin/providers - Create new provider
  - PATCH /llm/admin/providers/:id - Update provider
  - DELETE /llm/admin/providers/:id - Delete provider
  - POST /llm/admin/providers/:id/test - Test connection
  - POST /llm/admin/reload - Reload from database
- Updated llm-manager.service.ts to support OpenAI and Claude providers
- Added comprehensive test suite with 97.95% coverage
- Proper validation, error handling, and type safety

All tests pass. Pre-commit hooks pass.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/llm/dto/index.ts

@@ -1,2 +1,3 @@
 export * from "./chat.dto";
 export * from "./embed.dto";
+export * from "./provider-admin.dto";

apps/api/src/llm/dto/provider-admin.dto.ts

@@ -0,0 +1,169 @@
+import { IsString, IsIn, IsOptional, IsBoolean, IsUUID, IsObject } from "class-validator";
+import type { JsonValue } from "@prisma/client/runtime/library";
+
+/**
+ * DTO for creating a new LLM provider instance.
+ *
+ * @example
+ * ```typescript
+ * const dto: CreateLlmProviderDto = {
+ *   providerType: "ollama",
+ *   displayName: "Local Ollama",
+ *   config: {
+ *     endpoint: "http://localhost:11434",
+ *     timeout: 30000
+ *   },
+ *   isDefault: true,
+ *   isEnabled: true
+ * };
+ * ```
+ */
+export class CreateLlmProviderDto {
+  /**
+   * Provider type (ollama, openai, or claude)
+   */
+  @IsString()
+  @IsIn(["ollama", "openai", "claude"])
+  providerType!: string;
+
+  /**
+   * Human-readable display name for the provider
+   */
+  @IsString()
+  displayName!: string;
+
+  /**
+   * User ID for user-specific providers (null for system-level)
+   */
+  @IsOptional()
+  @IsUUID()
+  userId?: string;
+
+  /**
+   * Provider-specific configuration (endpoint, apiKey, etc.)
+   */
+  @IsObject()
+  config!: JsonValue;
+
+  /**
+   * Whether this is the default provider
+   */
+  @IsOptional()
+  @IsBoolean()
+  isDefault?: boolean;
+
+  /**
+   * Whether this provider is enabled
+   */
+  @IsOptional()
+  @IsBoolean()
+  isEnabled?: boolean;
+}
+
+/**
+ * DTO for updating an existing LLM provider instance.
+ * All fields are optional - only provided fields will be updated.
+ *
+ * @example
+ * ```typescript
+ * const dto: UpdateLlmProviderDto = {
+ *   displayName: "Updated Ollama",
+ *   isEnabled: false
+ * };
+ * ```
+ */
+export class UpdateLlmProviderDto {
+  /**
+   * Human-readable display name for the provider
+   */
+  @IsOptional()
+  @IsString()
+  displayName?: string;
+
+  /**
+   * Provider-specific configuration (endpoint, apiKey, etc.)
+   */
+  @IsOptional()
+  @IsObject()
+  config?: JsonValue;
+
+  /**
+   * Whether this is the default provider
+   */
+  @IsOptional()
+  @IsBoolean()
+  isDefault?: boolean;
+
+  /**
+   * Whether this provider is enabled
+   */
+  @IsOptional()
+  @IsBoolean()
+  isEnabled?: boolean;
+}
+
+/**
+ * Response DTO for LLM provider instance.
+ * Matches the Prisma LlmProviderInstance model.
+ *
+ * @example
+ * ```typescript
+ * const response: LlmProviderResponseDto = {
+ *   id: "provider-123",
+ *   providerType: "ollama",
+ *   displayName: "Local Ollama",
+ *   userId: null,
+ *   config: { endpoint: "http://localhost:11434" },
+ *   isDefault: true,
+ *   isEnabled: true,
+ *   createdAt: new Date(),
+ *   updatedAt: new Date()
+ * };
+ * ```
+ */
+export class LlmProviderResponseDto {
+  /**
+   * Unique identifier for the provider instance
+   */
+  id!: string;
+
+  /**
+   * Provider type (ollama, openai, or claude)
+   */
+  providerType!: string;
+
+  /**
+   * Human-readable display name for the provider
+   */
+  displayName!: string;
+
+  /**
+   * User ID for user-specific providers (null for system-level)
+   */
+  userId?: string | null;
+
+  /**
+   * Provider-specific configuration (endpoint, apiKey, etc.)
+   */
+  config!: JsonValue;
+
+  /**
+   * Whether this is the default provider
+   */
+  isDefault!: boolean;
+
+  /**
+   * Whether this provider is enabled
+   */
+  isEnabled!: boolean;
+
+  /**
+   * Timestamp when the provider was created
+   */
+  createdAt!: Date;
+
+  /**
+   * Timestamp when the provider was last updated
+   */
+  updatedAt!: Date;
+}