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/factory.py

@@ -0,0 +1,50 @@
+import asyncio
+from contextlib import suppress
+from cryptography.fernet import Fernet
+from sanic import Sanic
+from sanic_ext import Extend
+
+from .managers import ConnectionManager
+from .stores import MessageStore, UserSessionStore
+from .logger import logger
+
+from .routes import register_routes
+
+
+def create_app() -> Sanic:
+    app = Sanic("cmd-chat-server")
+    Extend(app)
+
+    app.ctx.message_store = MessageStore()
+    app.ctx.session_store = UserSessionStore()
+    app.ctx.connection_manager = ConnectionManager()
+    app.ctx.admin_password = None
+    app.ctx.fernet_key = Fernet.generate_key()
+    app.ctx.cleanup_task = None
+
+    register_lifecycle(app)
+    register_routes(app)
+
+    return app
+
+
+def register_lifecycle(app: Sanic) -> None:
+    @app.before_server_start
+    async def setup(app: Sanic):
+        logger.info("Server starting...")
+        app.ctx.cleanup_task = asyncio.create_task(cleanup_stale_sessions(app))
+
+    @app.after_server_stop
+    async def teardown(app: Sanic):
+        logger.info("Server shutting down...")
+        if app.ctx.cleanup_task:
+            app.ctx.cleanup_task.cancel()
+            with suppress(asyncio.CancelledError):
+                await app.ctx.cleanup_task
+
+
+async def cleanup_stale_sessions(app: Sanic) -> None:
+    while True:
+        with suppress(asyncio.CancelledError):
+            await asyncio.sleep(300)
+            await app.ctx.session_store.cleanup_stale()