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/server/managers.py

@@ -0,0 +1,48 @@
+import asyncio
+from typing import Optional
+from sanic import Websocket
+from .logger import logger
+
+
+class ConnectionManager:
+    def __init__(self):
+        self.active_connections: dict[str, Websocket] = {}
+        self._lock = asyncio.Lock()
+
+    async def connect(self, user_id: str, websocket: Websocket) -> None:
+        async with self._lock:
+            self.active_connections[user_id] = websocket
+        logger.info(f"Client connected: {user_id}")
+
+    async def disconnect(self, user_id: str) -> None:
+        async with self._lock:
+            if user_id in self.active_connections:
+                del self.active_connections[user_id]
+        logger.info(f"Client disconnected: {user_id}")
+
+    async def broadcast(self, message: str, exclude_user: Optional[str] = None) -> None:
+        async with self._lock:
+            disconnected = []
+            for user_id, connection in list(self.active_connections.items()):
+                if exclude_user and user_id == exclude_user:
+                    continue
+                try:
+                    await connection.send(message)
+                except Exception as e:
+                    logger.warning(f"Failed to send message to {user_id}: {e}")
+                    disconnected.append(user_id)
+
+            for user_id in disconnected:
+                if user_id in self.active_connections:
+                    del self.active_connections[user_id]
+
+    async def send_personal(self, user_id: str, message: str) -> bool:
+        async with self._lock:
+            if connection := self.active_connections.get(user_id):
+                try:
+                    await connection.send(message)
+                    return True
+                except Exception as e:
+                    logger.warning(f"Failed to send personal message to {user_id}: {e}")
+                    return False
+        return False