feat(admin): add restore dismissed alerts flow

Admins can now surface dismissed alert types without waiting for the
underlying data to change. Adds a collapsible "Restore dismissed"
section below the active alerts with per-type checkboxes.

- ALERT_METADATA map in adminAlerts.js as the single source of truth
  for slug → title/severity; detectors refactored to reference it
- GET /api/admin/alerts/dismissed returns this admin's dismissals
  joined with metadata (title, severity, dismissedAt)
- POST /api/admin/alerts/restore deletes dismissals by alertType[],
  returns the deleted count
- AdminAlertsPanel fetches both active + dismissed; stays visible
  when either is non-empty; checkboxes + "Restore selected" button
- adminAlertRestoreSchema validates the POST body against the enum
- Auth guards test covers both new routes

app/components/admin/AdminAlertsPanel.vue

@@ -1,7 +1,8 @@
 <!-- app/components/admin/AdminAlertsPanel.vue -->
 <template>
-  <div v-if="visibleAlerts.length" class="alerts-panel">
+  <div v-if="hasContent" class="alerts-panel">
     <div class="section-label">Needs Attention</div>
+
     <div
       v-for="alert in visibleAlerts"
       :key="alert.type"
@@ -33,16 +34,77 @@
         </li>
       </ul>
     </div>
+
+    <div v-if="!visibleAlerts.length" class="empty-active">
+      No active alerts.
+    </div>
+
+    <div v-if="dismissedAlerts.length" class="restore-section">
+      <button
+        v-if="!restoreOpen"
+        type="button"
+        class="restore-toggle"
+        @click="restoreOpen = true"
+      >
+        Restore dismissed ({{ dismissedAlerts.length }})
+      </button>
+      <div v-else class="restore-panel">
+        <div class="section-label restore-label">Restore dismissed alerts</div>
+        <ul class="restore-list">
+          <li v-for="d in dismissedAlerts" :key="d.alertType">
+            <label class="restore-option">
+              <input
+                v-model="selectedRestore"
+                type="checkbox"
+                :value="d.alertType"
+              />
+              <span>{{ d.title }}</span>
+              <span class="restore-when">dismissed {{ formatDismissedAt(d.dismissedAt) }}</span>
+            </label>
+          </li>
+        </ul>
+        <div class="restore-actions">
+          <button
+            type="button"
+            class="dismiss-btn"
+            :disabled="!selectedRestore.length || restoring"
+            @click="restoreSelected"
+          >
+            Restore selected
+          </button>
+          <button
+            type="button"
+            class="dismiss-btn"
+            @click="cancelRestore"
+          >
+            Cancel
+          </button>
+        </div>
+      </div>
+    </div>
   </div>
 </template>
 
 <script setup>
 const maxItems = 5
 const dismissing = reactive({})
+const restoreOpen = ref(false)
+const selectedRestore = ref([])
+const restoring = ref(false)
 
-const { data, refresh } = await useFetch('/api/admin/alerts', { default: () => ({ alerts: [] }) })
+const { data, refresh } = await useFetch('/api/admin/alerts', {
+  default: () => ({ alerts: [] })
+})
+const { data: dismissedData, refresh: refreshDismissed } = await useFetch(
+  '/api/admin/alerts/dismissed',
+  { default: () => ({ dismissed: [] }) }
+)
 
 const visibleAlerts = computed(() => data.value?.alerts || [])
+const dismissedAlerts = computed(() => dismissedData.value?.dismissed || [])
+const hasContent = computed(
+  () => visibleAlerts.value.length > 0 || dismissedAlerts.value.length > 0
+)
 
 function displayItems(alert) {
   return alert.items.slice(0, maxItems)
@@ -55,18 +117,51 @@ async function dismissAlert(alert) {
       method: 'POST',
       body: { alertType: alert.type, signature: alert.signature }
     })
-    // Optimistic local removal
-    data.value = {
-      alerts: visibleAlerts.value.filter((a) => a.type !== alert.type)
-    }
+    // Refetch both lists so the dismissed alert appears in the restore list
+    await Promise.all([refresh(), refreshDismissed()])
   } catch (err) {
     console.error('Failed to dismiss alert', err)
-    // On error, refetch to get authoritative state
     await refresh()
   } finally {
     dismissing[alert.type] = false
   }
 }
+
+async function restoreSelected() {
+  if (!selectedRestore.value.length) return
+  restoring.value = true
+  try {
+    await $fetch('/api/admin/alerts/restore', {
+      method: 'POST',
+      body: { alertTypes: selectedRestore.value }
+    })
+    selectedRestore.value = []
+    restoreOpen.value = false
+    await Promise.all([refresh(), refreshDismissed()])
+  } catch (err) {
+    console.error('Failed to restore alerts', err)
+  } finally {
+    restoring.value = false
+  }
+}
+
+function cancelRestore() {
+  selectedRestore.value = []
+  restoreOpen.value = false
+}
+
+function formatDismissedAt(value) {
+  if (!value) return ''
+  const d = new Date(value)
+  const now = Date.now()
+  const diffMin = Math.round((now - d.getTime()) / 60000)
+  if (diffMin < 1) return 'just now'
+  if (diffMin < 60) return `${diffMin}m ago`
+  const diffH = Math.round(diffMin / 60)
+  if (diffH < 24) return `${diffH}h ago`
+  const diffD = Math.round(diffH / 24)
+  return `${diffD}d ago`
+}
 </script>
 
 <style scoped>
@@ -170,4 +265,76 @@ async function dismissAlert(alert) {
   color: var(--text-faint);
   font-style: italic;
 }
+
+.empty-active {
+  font-size: 12px;
+  color: var(--text-faint);
+  font-style: italic;
+  padding: 4px 0 8px;
+}
+
+.restore-section {
+  margin-top: 12px;
+  padding-top: 12px;
+  border-top: 1px dashed var(--border);
+}
+
+.restore-toggle {
+  background: none;
+  border: none;
+  padding: 0;
+  font-size: 11px;
+  color: var(--text-dim);
+  cursor: pointer;
+  font-family: inherit;
+  text-decoration: underline dashed;
+  text-underline-offset: 3px;
+}
+
+.restore-toggle:hover {
+  color: var(--candle);
+}
+
+.restore-panel {
+  padding: 4px 0;
+}
+
+.restore-label {
+  margin-bottom: 8px;
+}
+
+.restore-list {
+  list-style: none;
+  padding: 0;
+  margin: 0 0 10px;
+}
+
+.restore-list li {
+  padding: 4px 0;
+}
+
+.restore-option {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  font-size: 12px;
+  color: var(--text);
+  cursor: pointer;
+}
+
+.restore-option input[type='checkbox'] {
+  accent-color: var(--candle);
+  cursor: pointer;
+}
+
+.restore-when {
+  color: var(--text-faint);
+  font-size: 11px;
+  margin-left: auto;
+}
+
+.restore-actions {
+  display: flex;
+  gap: 8px;
+}
 </style>