feat add remote hand tracking backend

backend/connection_manager.py

@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+from uuid import uuid4
+
+from fastapi import WebSocket
+
+
+@dataclass
+class ClientConnection:
+    id: str
+    websocket: WebSocket
+    is_processing: bool = False
+    last_frame_at: float = 0.0
+    metadata: dict[str, Any] = field(default_factory=dict)
+
+
+class ConnectionManager:
+    def __init__(self) -> None:
+        self._connections: dict[str, ClientConnection] = {}
+
+    @property
+    def count(self) -> int:
+        return len(self._connections)
+
+    async def connect(self, websocket: WebSocket) -> ClientConnection:
+        await websocket.accept()
+        connection = ClientConnection(id=str(uuid4()), websocket=websocket)
+        self._connections[connection.id] = connection
+        return connection
+
+    def disconnect(self, connection: ClientConnection) -> None:
+        self._connections.pop(connection.id, None)
+
+    async def send(self, connection: ClientConnection, payload: dict[str, Any]) -> None:
+        await connection.websocket.send_json(payload)