fix(monitoring): prevent Vault crash and DNS null error

- Vault: Wrap resp.json() in a try-except block to prevent JSONDecodeError when hitting an HTML error page (e.g. 502/503). This prevents the entire agent from crashing and missing heartbeats.
- Uptime Kuma DNS: Explicitly set dns_resolve_server to 1.1.1.1 in Python API payload to prevent Uptime Kuma backend from crashing on null properties.

health-agent/scripts/setup_uptime_kuma.py

@@ -261,6 +261,7 @@ def setup_uptime_kuma(dry_run=False, only=None):
                     "hostname": hostname,
                     "port": 53,
                     "accepted_statuscodes": ["200-299"],
+                    "dns_resolve_server": "1.1.1.1",
                     "dns_resolve_type": dns_resolve_type,
                     "interval": interval,
                 }
@@ -280,6 +281,7 @@ def setup_uptime_kuma(dry_run=False, only=None):
                         "hostname": hostname,
                         "port": 53,
                         "accepted_statuscodes": ["200-299"],
+                        "dns_resolve_server": "1.1.1.1",
                         "dns_resolve_type": dns_resolve_type,
                         "interval": interval,
                     }

health-agent/src/health_agent/checks/http.py

@@ -140,11 +140,14 @@ def check_vault():
         max_ping = max(max_ping, ms)
         
         if resp is not None:
+            try:
                 data = resp.json()
                 if not data.get("sealed"):
                     unsealed_count += 1
                 else:
                     errors.append(f"{node} SEALED")
+            except Exception as e:
+                errors.append(f"{node} invalid response: {resp.status_code}")
         else:
             errors.append(f"{node} unreachable: {err}")