- Create chatFileRoutes with upload, list, content, references, attach endpoints
- Wire into app.ts after assetRoutes, export from routes/index.ts
- Real tests replacing todo stubs in chat-file-routes.test.ts
- Add ChatFile, ChatFileReference, ChatFileUploadResponse, ChatFileListResponse interfaces to types/chat.ts
- Add optional files?: ChatFile[] field to ChatMessage interface
- Add uploadChatFileSchema and createFileReferenceSchema Zod validators to validators/chat.ts
- Re-export all new types and validators from shared/src/index.ts
- Create test stubs for chat-file-service.test.ts and chat-file-routes.test.ts with it.todo() entries
