fix: P2 API hardening — unbounded SELECTs, export audit log, header injection, empty-key guard

- export: add .limit(10000), sanitize filename, write_audit_log on every export
- stats: add .limit(10000) to aggregation query
- settings POST: reject empty string values to prevent silent key deletion

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

app/api/dashboard/export/route.ts

@@ -31,6 +31,7 @@ export async function GET(request: NextRequest) {
       sites (name), zones (name)
     `)
     .order('reported_at', { ascending: false })
+    .limit(10000)
 
   const rows = incidents ?? []
 
@@ -58,7 +59,15 @@ export async function GET(request: NextRequest) {
   })
 
   const csv = rowsToCsv(headers, csvRows)
-  const filename = `incidents-${role}-${new Date().toISOString().split('T')[0]}.csv`
+  const safeRole = role.replace(/[^a-z0-9]/gi, '')
+  const filename = `incidents-${safeRole}-${new Date().toISOString().split('T')[0]}.csv`
+
+  await supabase.rpc('write_audit_log', {
+    p_table_name: 'incidents',
+    p_record_id: user.id,
+    p_action: 'export_csv',
+    p_new_value: { role, row_count: rows.length } as never,
+  })
 
   return new NextResponse(csv, {
     status: 200,

app/api/dashboard/stats/route.ts

@@ -15,6 +15,7 @@ export async function GET() {
   const { data: incidents, error } = await supabase
     .from('incidents')
     .select('id, status, incident_type, sites (name)')
+    .limit(10000)
 
   if (error) return NextResponse.json({ error: 'Failed to fetch stats' }, { status: 500 })