feat(admin): add adminAlerts module shell with thresholds and signature helper

server/utils/adminAlerts.js

@@ -0,0 +1,39 @@
+import { createHash } from 'node:crypto'
+import Member from '../models/member.js'
+import Event from '../models/event.js'
+import PreRegistration from '../models/preRegistration.js'
+import TagSuggestion from '../models/tagSuggestion.js'
+import AdminAlertDismissal, { ADMIN_ALERT_TYPES } from '../models/adminAlertDismissal.js'
+import { connectDB } from './mongoose.js'
+
+export const ALERT_THRESHOLDS = {
+  NO_SLACK_DAYS: 7,
+  STUCK_PAYMENT_DAYS: 7,
+  PREREG_SELECTED_DAYS: 3,
+  DRAFT_IMMINENT_DAYS: 14,
+  NEAR_CAPACITY_RATIO: 0.8
+}
+
+const DAY_MS = 24 * 60 * 60 * 1000
+
+function daysAgo(days) {
+  return new Date(Date.now() - days * DAY_MS)
+}
+
+function daysSince(date) {
+  if (!date) return null
+  return Math.floor((Date.now() - new Date(date).getTime()) / DAY_MS)
+}
+
+export function computeSignature(ids) {
+  const normalized = ids
+    .map((id) => (id == null ? '' : String(id)))
+    .sort()
+  const hash = createHash('sha1')
+  hash.update(JSON.stringify(normalized))
+  return hash.digest('hex')
+}
+
+// Alert functions land here in tasks 4–7.
+
+// Aggregator lands in task 8.