fix: P1 API security hardening — rate limits, auth guards, duplicate prevention

- verify/route.ts: setDate → setUTCDate to avoid timezone off-by-one on recheck date
- triage-suggest, rca-draft, quality-check: 60s per-user rate limit via audit_log
- quality-check: add write_audit_log (was missing, CLAUDE.md violation)
- investigation POST: 409 if investigation already exists for incident
- incidents POST: 60s per-user rate limit via audit_log
- addenda GET: restrict to hse/admin/supervisor roles
- dashboard/stats GET: restrict to hse/admin/management roles

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CPf5Rc8QPx6V8KLEEgfKEQ

app/api/incidents/ai/quality-check/route.ts

@@ -10,6 +10,16 @@ export async function POST(request: NextRequest) {
   const { data: { user }, error: authError } = await supabase.auth.getUser()
   if (authError || !user) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
 
+  const since = new Date(Date.now() - 60_000).toISOString()
+  const { count: recentCount } = await supabase
+    .from('audit_log')
+    .select('id', { count: 'exact', head: true })
+    .eq('changed_by', user.id)
+    .eq('action', 'ai_quality_check')
+    .gte('changed_at', since)
+  if ((recentCount ?? 0) > 0)
+    return NextResponse.json({ error: 'Rate limited — please wait 60 seconds' }, { status: 429 })
+
   const anthropicKey = await getApiKey(supabase, 'ANTHROPIC_API_KEY')
   const anthropic = createAnthropicClient(anthropicKey)
 
@@ -81,5 +91,13 @@ Score 1–10 based on: specificity (location, time, persons involved), completen
   ) {
     return NextResponse.json({ error: 'AI returned unexpected structure' }, { status: 500 })
   }
+
+  await supabase.rpc('write_audit_log', {
+    p_table_name: 'incidents',
+    p_record_id: user.id,
+    p_action: 'ai_quality_check',
+    p_new_value: { score: input.score, passes: input.passes, model: 'claude-opus-4-8' } as never,
+  })
+
   return NextResponse.json(input)
 }