feat: add WebSocket announce manager

Made-with: Cursor

src/ntr_fetcher/websocket.py

@@ -0,0 +1,37 @@
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class AnnounceManager:
+    def __init__(self):
+        self._subscribers: list = []
+
+    @property
+    def subscriber_count(self) -> int:
+        return len(self._subscribers)
+
+    def add_subscriber(self, websocket) -> None:
+        self._subscribers.append(websocket)
+        logger.info("Subscriber connected (%d total)", self.subscriber_count)
+
+    def remove_subscriber(self, websocket) -> None:
+        self._subscribers = [ws for ws in self._subscribers if ws is not websocket]
+        logger.info("Subscriber disconnected (%d total)", self.subscriber_count)
+
+    async def broadcast(self, message: dict) -> None:
+        dead = []
+        for ws in self._subscribers:
+            try:
+                await ws.send_json(message)
+            except Exception:
+                dead.append(ws)
+                logger.warning("Removing dead subscriber")
+        for ws in dead:
+            self.remove_subscriber(ws)
+
+    async def broadcast_status(self) -> None:
+        await self.broadcast({
+            "type": "status",
+            "subscribers": self.subscriber_count,
+        })