Implement message reporting endpoint and moderation review queue (US-4)

- POST /api/chat/messages/{message_id}/report for reporting messages with category/reason
- Idempotent duplicate report rejection (409)
- GET /api/moderation/reports for queue listing (restricted to moderators/admins)
- POST /api/moderation/reports/{id}/resolve supporting dismiss, remove, warn, ban actions
- Audit fields (moderator_id, resolved_at, action) recorded on resolution
- Added 9 integration tests in backend/tests/test_chat_reports.py (all passing)

backend/app/main.py

@@ -6,7 +6,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.config import settings
-from app.routers import auth, users, worlds, assets, avatar, world_content, internal, presence, groups, social_friends, profiles, chat_dm
+from app.routers import auth, users, worlds, assets, avatar, world_content, internal, presence, groups, social_friends, profiles, chat_dm, chat_reports
 
 
 from app.services.game_servers import supervisor
@@ -49,6 +49,8 @@ app.include_router(groups.router, prefix="/api/groups", tags=["groups"])
 app.include_router(social_friends.router, prefix="/api/friends", tags=["friends"])
 app.include_router(profiles.router, prefix="/api/profile", tags=["profile"])
 app.include_router(chat_dm.router, prefix="/api/chat/dm", tags=["chat-dm"])
+app.include_router(chat_reports.chat_router, prefix="/api/chat", tags=["chat-reports"])
+app.include_router(chat_reports.moderation_router, prefix="/api/moderation", tags=["moderation"])
 
 
 @app.get("/api/health")