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/helpers.py

@@ -0,0 +1,58 @@
+from datetime import datetime, timezone
+from typing import Optional
+from dataclasses import asdict
+import json
+from sanic import Sanic, Request, response, Websocket
+
+
+def utcnow() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+def verify_password(password: Optional[str], expected: Optional[str]) -> bool:
+    if not expected:
+        return True
+    return password == expected
+
+
+def get_client_ip(request: Request) -> str:
+    if forwarded := request.headers.get("x-forwarded-for"):
+        return forwarded.split(",")[0].strip()
+    return request.ip
+
+
+def get_param(request: Request, name: str) -> Optional[str]:
+    return request.args.get(name) or request.form.get(name)
+
+
+def require_auth(request: Request, app: Sanic) -> Optional[response.HTTPResponse]:
+    if not verify_password(get_param(request, "password"), app.ctx.admin_password):
+        return response.text("Unauthorized", status=401)
+    return None
+
+
+async def send_state(ws: Websocket, app: Sanic) -> None:
+    messages = await app.ctx.message_store.get_all()
+    users = await app.ctx.session_store.get_all()
+    await ws.send(
+        json.dumps(
+            {
+                "type": "init",
+                "messages": [asdict(m) for m in messages],
+                "users": [
+                    {"user_id": u.user_id, "username": u.username} for u in users
+                ],
+            }
+        )
+    )
+
+
+def extract_pubkey(request: Request) -> Optional[bytes]:
+    if files := request.files.get("pubkey"):
+        file = files[0] if isinstance(files, list) else files
+        return file.body
+    if raw := request.form.get("pubkey"):
+        return raw.encode() if isinstance(raw, str) else raw
+    if raw := request.args.get("pubkey"):
+        return raw.encode() if isinstance(raw, str) else raw
+    return None