De-hardcode ticket URL and cluster name; improve diagnostic polling UX

app.py:
- Context processor injects config.ticket_api.web_url into all templates
  (falls back to 'http://t.lotusguild.org/ticket/' if not set in config)

templates/base.html:
- Inject GANDALF_CONFIG JS global with ticket_web_url before app.js loads

static/app.js:
- Use GANDALF_CONFIG.ticket_web_url instead of hardcoded domain

templates/index.html:
- Use {{ config.ticket_api.web_url }} Jinja var instead of hardcoded domain

monitor.py:
- CLUSTER_NAME constant kept as default; NetworkMonitor now reads cluster_name
  from config monitor.cluster_name, falling back to the constant
- All CLUSTER_NAME references inside class methods replaced with self.cluster_name

templates/inspector.html:
- pollDiagnostic() .catch() now clears interval and shows error message instead
  of silently ignoring network failures during active polling

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

templates/inspector.html

@@ -451,7 +451,11 @@ function pollDiagnostic(jobId, statusEl, resultsEl) {
         renderDiagnosticResults(resp.result, resultsEl);
       }
     })
-    .catch(() => {});
+    .catch(() => {
+      clearInterval(_diagPollTimer);
+      _diagPollTimer = null;
+      statusEl.textContent = 'Error: lost connection while collecting diagnostics.';
+    });
   }, 2000);
 }