feat: complete client-server architecture refactoring

Server:
- Split into views, routes, helpers, models modules
- Merged /ws/talk and /ws/update into single /ws/chat endpoint
- Replaced polling with push-based broadcast model
- Added username uniqueness validation on connect
- Fixed run_server arguments bug (workers parameter)
- Removed deprecated loop argument from Sanic listeners
- Replaced datetime.utcnow() with timezone-aware datetime.now(timezone.utc)

Client:
- Rewrote client as single-file module
- Migrated from websocket-client to websockets (asyncio)
- Fixed websocket-client conflict with asyncio event loop on Windows
- Added progress indicators for key generation, exchange, connection
- Added animated 3D spinning cube in UI
- Updated RSA key from 512 to 2048 bits

CLI:
- Removed unnecessary asyncio.run() wrapper
- Simplified entry point

requirements.txt

@@ -6,4 +6,6 @@ colorama
 pydantic
 websocket-client
 flask 
-rich
+rich
+sanic_ext
+websockets