feat(feedback): implement user feedback collection system with email reporting

Backend:
- Add user_feedback table with RLS policy
- Create feedback submission API (multipart/form-data)
- Implement xlsx report generation with embedded images
- Add scheduled email delivery via Feishu SMTP
- Create HTML email templates (daily_report, no_feedback)

Frontend:
- Add feedback screen with type selection and image picker
- Support anonymous submission via skipAuth flag
- Collect device info and app version

Protocol:
- Document feedback API contract and error codes
- Update http-error-codes.md with FEEDBACK_* codes

backend/src/v1/router.py

@@ -4,6 +4,7 @@ from fastapi import APIRouter
 
 from v1.agent.router import router as agent_router
 from v1.auth.router import router as auth_router
+from v1.feedback.router import router as feedback_router
 from v1.invite.router import router as invite_router
 from v1.notifications.router import router as notifications_router
 from v1.points.router import router as points_router
@@ -13,6 +14,7 @@ from v1.users.router import router as users_router
 router = APIRouter(prefix="/api/v1")
 router.include_router(auth_router)
 router.include_router(agent_router)
+router.include_router(feedback_router)
 router.include_router(invite_router)
 router.include_router(notifications_router)
 router.include_router(points_router)