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

cmd_chat/client/core/abs/abs_crypto.py

@@ -1,5 +1,6 @@
 from abc import ABC, abstractmethod
 
+
 class CryptoService(ABC):
 
     @abstractmethod

cmd_chat/client/core/abs/abs_renderer.py

@@ -2,10 +2,9 @@ from abc import ABC, abstractmethod
 
 
 class ClientRenderer(ABC):
-    # These attributes are expected to be provided by subclasses
-    # (typically via multiple inheritance with CryptoService)
+
     username: str
-    
+
     @abstractmethod
     def _decrypt(self, message: str) -> str:
         """Decrypt an encrypted message (provided by crypto mixin)."""