feat(v2): Add pkt_payload to DMs, update watchdog for single container

- Add pkt_payload column to direct_messages table for stable packet
  hash generation and Analyzer URL linking
- Update insert_direct_message() and DeviceManager to store pkt_payload
- Add test for DM pkt_payload storage (43 tests pass)
- Update watchdog to monitor only mc-webui (meshcore-bridge removed)
- USB reset trigger now fires for mc-webui container failures

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

tests/test_database.py

@@ -250,6 +250,16 @@ class TestDirectMessages:
         assert ack is not None
         assert ack['snr'] == -3.0
 
+    def test_dm_with_pkt_payload(self, db):
+        db.upsert_contact('cc', name='Charlie')
+        ts = int(time.time())
+        dm_id = db.insert_direct_message(
+            'cc', 'in', 'Hello', ts, pkt_payload='deadbeef01020304'
+        )
+        messages = db.get_dm_messages('cc')
+        assert len(messages) == 1
+        assert messages[0]['pkt_payload'] == 'deadbeef01020304'
+
 
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