fix: keep dashboard terminal sessions alive

Remove backend idle timeout enforcement so terminal sessions persist until the UI disconnects or the SSH process ends.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/backend/routers/terminal.py

@@ -10,7 +10,6 @@ import config
 logger = logging.getLogger(__name__)
 
 MAX_SESSIONS = 5
-IDLE_TIMEOUT = 30 * 60  # 30 minutes
 _active_sessions: set = set()
 
 HOSTS = {
@@ -95,18 +94,10 @@ async def ws_endpoint(websocket: WebSocket, host: str = Query("nas")):
                 pass
 
         read_task = asyncio.create_task(read_ssh())
-        last_activity = time.monotonic()
 
         try:
             while True:
-                try:
-                    msg = await asyncio.wait_for(websocket.receive(), timeout=60)
-                except asyncio.TimeoutError:
-                    if time.monotonic() - last_activity > IDLE_TIMEOUT:
-                        await websocket.close(code=1000, reason="Idle timeout")
-                        break
-                    continue
-                last_activity = time.monotonic()
+                msg = await websocket.receive()
                 if "bytes" in msg and msg["bytes"]:
                     data = msg["bytes"]
                     if data[0:1] == b"\x01" and len(data) == 5: