Move reranker to Serenity, add monitoring and mesh-mqtt-observer stacks

- ai: remove reranker service (moved to Serenity at 10.5.1.5:9787)
- ai: add LiteLLM reranker proxy entry for Serenity
- ai: configure OpenWebUI to use LiteLLM for reranking
- monitoring: add Grafana + Prometheus stack
- mesh-mqtt-observer: add new service
- automation, documents, meshtastic: misc updates

mesh-mqtt-observer/app/healthcheck.py

@@ -0,0 +1,25 @@
+import os
+import sys
+
+import psycopg
+
+
+def main() -> int:
+    dsn = os.getenv("DATABASE_URL")
+    if not dsn:
+        print("DATABASE_URL missing")
+        return 1
+
+    try:
+        with psycopg.connect(dsn, autocommit=True) as conn:
+            with conn.cursor() as cur:
+                cur.execute("SELECT 1")
+                cur.fetchone()
+        return 0
+    except Exception as exc:
+        print(exc)
+        return 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())