Add AI cost insights dashboard; rota-informed forecast method

AI Insights: a daily Claude-generated wage cost briefing covering
month-to-date pace vs budget, prior-month/prior-year comparison,
rota-vs-actual variance by department, a rota-informed forecast to
month-end, employee-level anomalies, and wage cost as a % of revenue.
Runs on a configurable daily schedule or on demand, gated by a manual
5-minute rate limit and a daily token budget. Uses the Anthropic key
configured centrally in Portal → Settings → Integrations.

Also includes the rota-vs-repeat-pattern forecast method (published/
draft rota tiers with same-weekday fallback) already built into the
Weekly/Monthly views, and adds a .gitignore for node_modules/dist.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/lib/aiInsight.tsx

@@ -0,0 +1,37 @@
+export function formatAge(iso: string): string {
+  const ms = Date.now() - new Date(iso).getTime()
+  const mins = Math.floor(ms / 60000)
+  if (mins < 1) return 'just now'
+  if (mins < 60) return `${mins}m ago`
+  const hours = Math.floor(mins / 60)
+  if (hours < 24) return `${hours}h ago`
+  return `${Math.floor(hours / 24)}d ago`
+}
+
+function escHtml(s: string): string {
+  return s
+    .replace(/&/g, '&amp;')
+    .replace(/</g, '&lt;')
+    .replace(/>/g, '&gt;')
+}
+
+export function renderContent(text: string) {
+  return text.split('\n').map((line, i) => {
+    const safe = escHtml(line)
+    const processed = safe.replace(/\*\*(.+?)\*\*/g, '<strong>$1</strong>')
+    if (line.startsWith('- ') || line.startsWith('* ')) {
+      return (
+        <div key={i} style={{ display: 'flex', gap: 8, marginBottom: 4 }}>
+          <span style={{ color: 'var(--gold)', flexShrink: 0 }}>•</span>
+          <span dangerouslySetInnerHTML={{ __html: processed.slice(2) }} />
+        </div>
+      )
+    }
+    if (line.startsWith('## ') || line.startsWith('# ')) {
+      const txt = line.replace(/^#+\s*/, '')
+      return <p key={i} style={{ fontWeight: 600, marginTop: 12, marginBottom: 6, color: 'var(--text-primary)' }}>{txt}</p>
+    }
+    if (line.trim() === '') return <div key={i} style={{ height: 8 }} />
+    return <p key={i} style={{ marginBottom: 4 }} dangerouslySetInnerHTML={{ __html: processed }} />
+  })
+}