feat: add a runtime diagnostics page

Adds GET /api/clouds/:cloud/diagnostics and a Diagnostics page in the
General nav. The report combines, in one call:

- runtime reachability, latency, version and edition from /_floci/health
- every service the runtime emulates, with the console pages backed by it
- per-console-service probes (the existing status check)
- EC2 instance containers from /_floci/diagnose
- console uptime, sign-in mode and active session count

Each source is optional, so a down runtime still yields a partial report.

packages/frontend/src/index.css

@@ -4261,6 +4261,104 @@ pre,
     gap: 14px;
 }
 
+.diagnostics {
+    display: grid;
+    gap: 14px;
+}
+
+.diagnostics .table-panel {
+    overflow-x: auto;
+}
+
+.diagnostics-section-header {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    justify-content: space-between;
+    gap: 10px;
+    padding: 12px 16px;
+    border-bottom: 1px solid var(--border);
+}
+
+.diagnostics-section-header h2 {
+    margin: 0;
+    color: var(--text-bright);
+    font-size: 14px;
+}
+
+.diagnostics-filters,
+.diagnostics-filter-group {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    gap: 6px;
+}
+
+.diagnostics-filters .input {
+    width: 180px;
+}
+
+.diagnostics-service-grid {
+    display: grid;
+    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
+    margin: 0;
+    padding: 0;
+    list-style: none;
+}
+
+.diagnostics-service {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    gap: 6px 8px;
+    min-width: 0;
+    padding: 9px 16px;
+    border-bottom: 1px solid var(--border-faint);
+    font-size: 12px;
+}
+
+.diagnostics-page-link {
+    padding: 1px 7px;
+    border: 1px solid var(--border);
+    border-radius: 999px;
+    color: var(--link);
+    font-size: 11px;
+    text-decoration: none;
+}
+
+.diagnostics-page-link:hover {
+    border-color: var(--link);
+}
+
+.diagnostics-facts {
+    display: grid;
+    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
+    margin: 0;
+}
+
+.diagnostics-facts div {
+    padding: 12px 16px;
+}
+
+.diagnostics-facts dt {
+    color: var(--text-2);
+    font-size: 11px;
+    font-weight: 700;
+    letter-spacing: 0.08em;
+    text-transform: uppercase;
+}
+
+.diagnostics-facts dd {
+    margin: 4px 0 0;
+    color: var(--text-bright);
+}
+
+@media (max-width: 520px) {
+    .diagnostics-filters .input {
+        width: 100%;
+    }
+}
+
 .console-provider-banner {
     display: flex;
     align-items: center;