feat: add admin dashboard with usage stats

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/App.css

@@ -4919,6 +4919,125 @@ html.theme-cupertino .events-scroll-container {
   padding-bottom: 8px;
 }
 
+.admin-page {
+  width: 100%;
+  max-width: 1200px;
+  min-height: 100vh;
+  margin: 0 auto;
+  padding: 24px;
+  box-sizing: border-box;
+  color: var(--app-text);
+  display: flex;
+  flex-direction: column;
+  gap: 24px;
+}
+
+.admin-header {
+  display: flex;
+  align-items: flex-start;
+  justify-content: space-between;
+  gap: 16px;
+  padding-bottom: 16px;
+  border-bottom: 1px solid var(--app-header-border);
+}
+
+.admin-header-left {
+  display: flex;
+  align-items: flex-start;
+  gap: 20px;
+  min-width: 0;
+}
+
+.admin-title {
+  margin: 0;
+  font-size: 24px;
+  font-weight: 700;
+  background: var(--app-accent-gradient);
+  -webkit-background-clip: text;
+  background-clip: text;
+  -webkit-text-fill-color: transparent;
+}
+
+.admin-subtitle {
+  margin: 6px 0 0;
+  font-size: 14px;
+  color: var(--app-text-muted);
+}
+
+.admin-main {
+  display: flex;
+  flex-direction: column;
+  gap: 24px;
+  width: 100%;
+}
+
+.admin-kpi-grid {
+  margin-top: 0;
+  grid-template-columns: repeat(3, minmax(0, 1fr));
+}
+
+.admin-controls {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 24px;
+  padding: 16px 20px;
+  border-radius: var(--app-radius-card);
+  border: 1px solid var(--app-border-subtle);
+  background: var(--app-surface);
+}
+
+.admin-control-group {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+  min-width: 0;
+}
+
+.admin-control-label {
+  font-size: 13px;
+  font-weight: 600;
+  color: var(--app-text-muted);
+}
+
+.admin-control-buttons {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 8px;
+}
+
+.admin-control-buttons .btn {
+  width: auto;
+  padding: 8px 16px;
+  font-size: 14px;
+}
+
+.admin-charts-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(min(100%, 320px), 1fr));
+  gap: 20px;
+}
+
+.dashboard-subtitle {
+  margin-top: 4px;
+  font-size: 14px;
+  color: var(--app-text-muted);
+}
+
+@media (max-width: 640px) {
+  .admin-page {
+    padding: 16px;
+  }
+
+  .admin-header-left {
+    flex-direction: column;
+    gap: 12px;
+  }
+
+  .admin-kpi-grid {
+    grid-template-columns: repeat(2, minmax(0, 1fr));
+  }
+}
+
 .stats-consumption-chart .stats-bar-column--grouped {
   display: inline-flex;
   white-space: normal;