fix(mqtt): wrap SUBSCRIBE packet ID instead of growing unbounded

self._pid was incremented on every _subscribe() call (i.e. every
connect/reconnect) but encoded as a 16-bit field via
pid.to_bytes(2, "big"), which only accepts 1-65535. A long-lived
bridge with frequent MQTT reconnects eventually overflowed the
counter, raising "OverflowError: int too big to convert" on every
subsequent connect attempt - including the manual "Connect" button,
which silently 500'd while the background poll loop kept reconnecting
regardless, making the bug easy to miss.

Wrap back to 1 at the 16-bit boundary instead of growing forever.

kobrax_client.py

@@ -371,7 +371,12 @@ class KobraXClient:
     def _subscribe(self, topic: str):
         with self._lock:
             pid = self._pid
-            self._pid += 1
+            # MQTT packet IDs are a 16-bit field (1-65535, 0 reserved) - wrap
+            # instead of growing unbounded, otherwise a long-lived bridge with
+            # frequent reconnects eventually overflows pid.to_bytes(2, "big")
+            # (OverflowError: int too big to convert), breaking every future
+            # connect attempt including the manual "Connect" button.
+            self._pid = 1 if self._pid >= 0xFFFF else self._pid + 1
             if self._sock is not None:
                 self._sock.sendall(_build_subscribe(topic, pid))
         log.info("SUB %s", topic)