fix: Caddy health check must hit /config/ not /

GET http://cell-caddy:2019/ returns 404 because Caddy's admin API has no
root handler.  The health monitor interpreted every response as a failure,
restarted Caddy every 3 minutes, and prevented ACME from ever completing.

/config/ returns 200 + the running config JSON whenever Caddy is up and
serving — that is the correct liveness indicator.

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

api/caddy_manager.py

@@ -500,9 +500,14 @@ class CaddyManager(BaseServiceManager):
         return False
 
     def check_caddy_health(self) -> bool:
-        """GET the Caddy admin API root.  Returns True on HTTP 200."""
+        """GET Caddy's config endpoint.  Returns True on HTTP 200.
+
+        Caddy's admin API has no root handler — GET / returns 404 even when
+        fully healthy.  GET /config/ returns 200 + the running config JSON
+        whenever Caddy is up and serving.
+        """
         try:
-            resp = requests.get(CADDY_ADMIN_URL + "/", timeout=5)
+            resp = requests.get(CADDY_ADMIN_URL + "/config/", timeout=5)
         except requests.RequestException as e:
             logger.debug("Caddy health check error: %s", e)
             return False