feat(#22): implement brain query API

- Create brain module with service, controller, and DTOs
- POST /api/brain/query - Structured queries for tasks, events, projects
- GET /api/brain/context - Get current workspace context for agents
- GET /api/brain/search - Search across all entities
- Support filters: status, priority, date ranges, assignee, etc.
- 41 tests covering service (27) and controller (14)
- Integrated with AuthGuard, WorkspaceGuard, PermissionGuard

apps/api/src/brain/brain.module.ts

@@ -0,0 +1,17 @@
+import { Module } from "@nestjs/common";
+import { BrainController } from "./brain.controller";
+import { BrainService } from "./brain.service";
+import { PrismaModule } from "../prisma/prisma.module";
+import { AuthModule } from "../auth/auth.module";
+
+/**
+ * Brain module
+ * Provides unified query interface for agents to access workspace data
+ */
+@Module({
+  imports: [PrismaModule, AuthModule],
+  controllers: [BrainController],
+  providers: [BrainService],
+  exports: [BrainService],
+})
+export class BrainModule {}