feat(#133): add workspace-scoped LLM configuration

Implement per-workspace LLM provider and personality configuration
with proper hierarchy (workspace > user > system fallback).

Schema:
- Add WorkspaceLlmSettings model with provider/personality FKs
- One-to-one relation with Workspace
- JSON settings field for extensibility

Service:
- getSettings: Retrieves/creates workspace settings
- updateSettings: Updates with null value support
- getEffectiveLlmProvider: Hierarchy-based provider selection
- getEffectivePersonality: Hierarchy-based personality selection

Endpoints:
- GET /workspaces/:id/settings/llm - Get settings
- PATCH /workspaces/:id/settings/llm - Update settings
- GET /workspaces/:id/settings/llm/effective-provider
- GET /workspaces/:id/settings/llm/effective-personality

Configuration hierarchy:
1. Workspace-configured provider/personality
2. User-specific provider (for providers)
3. System default fallback

Tests: 34 passing with 100% coverage

Fixes #133

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

apps/api/src/workspace-settings/workspace-settings.controller.ts

@@ -0,0 +1,58 @@
+import { Controller, Get, Patch, Body, Param, Request, UseGuards } from "@nestjs/common";
+import { WorkspaceSettingsService } from "./workspace-settings.service";
+import { UpdateWorkspaceSettingsDto } from "./dto";
+import { AuthGuard } from "../auth/guards/auth.guard";
+import type { AuthenticatedRequest } from "../common/types/user.types";
+
+/**
+ * Controller for workspace LLM settings endpoints
+ * All endpoints require authentication
+ */
+@Controller("workspaces/:workspaceId/settings/llm")
+@UseGuards(AuthGuard)
+export class WorkspaceSettingsController {
+  constructor(private readonly workspaceSettingsService: WorkspaceSettingsService) {}
+
+  /**
+   * GET /api/workspaces/:workspaceId/settings/llm
+   * Get workspace LLM settings
+   */
+  @Get()
+  async getSettings(@Param("workspaceId") workspaceId: string) {
+    return this.workspaceSettingsService.getSettings(workspaceId);
+  }
+
+  /**
+   * PATCH /api/workspaces/:workspaceId/settings/llm
+   * Update workspace LLM settings
+   */
+  @Patch()
+  async updateSettings(
+    @Param("workspaceId") workspaceId: string,
+    @Body() dto: UpdateWorkspaceSettingsDto
+  ) {
+    return this.workspaceSettingsService.updateSettings(workspaceId, dto);
+  }
+
+  /**
+   * GET /api/workspaces/:workspaceId/settings/llm/effective-provider
+   * Get effective LLM provider for workspace
+   */
+  @Get("effective-provider")
+  async getEffectiveProvider(
+    @Param("workspaceId") workspaceId: string,
+    @Request() req: AuthenticatedRequest
+  ) {
+    const userId = req.user?.id;
+    return this.workspaceSettingsService.getEffectiveLlmProvider(workspaceId, userId);
+  }
+
+  /**
+   * GET /api/workspaces/:workspaceId/settings/llm/effective-personality
+   * Get effective personality for workspace
+   */
+  @Get("effective-personality")
+  async getEffectivePersonality(@Param("workspaceId") workspaceId: string) {
+    return this.workspaceSettingsService.getEffectivePersonality(workspaceId);
+  }
+}