feat: add admin-only status page with cache stats

- New /api/dashboard/status endpoint (admin-only, 403 for non-admins)
- Returns server info (uptime, Node version, memory usage)
- Returns polling mode and interval
- Returns cache stats: entry count, total size, per-key breakdown
  with item count, size in KB, and TTL remaining
- Status button in admin controls header
- Collapsible status panel with grid layout
- Responsive: single column on mobile

public/style.css

@@ -731,6 +731,148 @@ body {
   margin-left: auto;
 }
 
+/* ===== Status Button ===== */
+.status-btn {
+  padding: 4px 12px;
+  border: 1px solid var(--border);
+  border-radius: 5px;
+  background: var(--surface);
+  color: var(--text-secondary);
+  cursor: pointer;
+  font-size: 0.8rem;
+  font-weight: 500;
+  transition: background 0.2s, color 0.2s;
+}
+
+.status-btn:hover {
+  background: var(--accent);
+  color: white;
+  border-color: var(--accent);
+}
+
+/* ===== Status Panel ===== */
+.status-panel {
+  background: var(--surface);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  padding: 20px;
+  margin-bottom: 16px;
+  box-shadow: 0 2px 4px var(--shadow);
+}
+
+.status-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: 16px;
+}
+
+.status-header h3 {
+  margin: 0;
+  color: var(--text-primary);
+  font-size: 1.1rem;
+}
+
+.status-close {
+  background: none;
+  border: none;
+  font-size: 1.4rem;
+  color: var(--text-secondary);
+  cursor: pointer;
+  padding: 0 4px;
+  line-height: 1;
+}
+
+.status-close:hover {
+  color: var(--text-primary);
+}
+
+.status-grid {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 16px;
+}
+
+.status-card {
+  background: var(--background);
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  padding: 14px;
+}
+
+.status-card-wide {
+  grid-column: 1 / -1;
+}
+
+.status-card-title {
+  font-weight: 600;
+  font-size: 0.85rem;
+  color: var(--text-primary);
+  margin-bottom: 10px;
+  padding-bottom: 6px;
+  border-bottom: 1px solid var(--border);
+}
+
+.status-row {
+  display: flex;
+  justify-content: space-between;
+  padding: 3px 0;
+  font-size: 0.8rem;
+  color: var(--text-secondary);
+}
+
+.status-row span:last-child {
+  font-weight: 500;
+  color: var(--text-primary);
+}
+
+.status-table {
+  width: 100%;
+  border-collapse: collapse;
+  font-size: 0.78rem;
+}
+
+.status-table th {
+  text-align: left;
+  padding: 4px 8px;
+  color: var(--text-secondary);
+  font-weight: 600;
+  font-size: 0.7rem;
+  text-transform: uppercase;
+  letter-spacing: 0.3px;
+  border-bottom: 1px solid var(--border);
+}
+
+.status-table td {
+  padding: 5px 8px;
+  color: var(--text-primary);
+  border-bottom: 1px solid var(--border);
+}
+
+.status-table code {
+  font-size: 0.75rem;
+  background: var(--surface);
+  padding: 1px 4px;
+  border-radius: 3px;
+}
+
+.status-expired {
+  color: #c62828;
+  font-weight: 600;
+  font-size: 0.7rem;
+}
+
+.status-loading, .status-error {
+  text-align: center;
+  padding: 20px;
+  color: var(--text-secondary);
+  font-size: 0.9rem;
+}
+
+.status-error {
+  color: #c62828;
+}
+
 /* ===== Mobile ===== */
 @media (max-width: 768px) {
   .app-header {
@@ -760,4 +902,8 @@ body {
   .progress-container {
     flex-wrap: wrap;
   }
+
+  .status-grid {
+    grid-template-columns: 1fr;
+  }
 }