feat(#29): implement cron job configuration

- Add CronSchedule model to Prisma schema
- Implement CronService with CRUD operations
- Add REST API endpoints for cron management
- Create MoltBot plugin skill definition (SKILL.md)
- TDD: 9 passing tests for CronService

apps/api/src/app.module.ts

@@ -17,6 +17,7 @@ import { UsersModule } from "./users/users.module";
 import { WebSocketModule } from "./websocket/websocket.module";
 import { LlmModule } from "./llm/llm.module";
 import { BrainModule } from "./brain/brain.module";
+import { CronModule } from "./cron/cron.module";
 
 @Module({
   imports: [
@@ -36,6 +37,7 @@ import { BrainModule } from "./brain/brain.module";
     WebSocketModule,
     LlmModule,
     BrainModule,
+    CronModule,
   ],
   controllers: [AppController],
   providers: [AppService],