fix: use TCP socket probe instead of ping for LAN detection

dashboard/backend/main.py

@@ -119,14 +119,14 @@ async def client_ip(request: Request):
     ip = request.client.host
     if ip.startswith("192.168.31."):
         return {"ip": ip, "lan": True}
-    # Tailscale client — check if Mac is reachable on LAN
     if ip.startswith("100."):
+        import socket
         try:
-            proc = await asyncio.create_subprocess_exec(
-                "ping", "-c", "1", "-W", "1", "192.168.31.1",
-                stdout=asyncio.subprocess.DEVNULL, stderr=asyncio.subprocess.DEVNULL,
-            )
-            return {"ip": ip, "lan": await asyncio.wait_for(proc.wait(), 2) == 0}
+            s = socket.socket()
+            s.settimeout(1)
+            s.connect(("192.168.31.1", 80))
+            s.close()
+            return {"ip": ip, "lan": True}
         except Exception:
             pass
     return {"ip": ip, "lan": False}