feat: implement FraudShield MVP — backend API + frontend alerts

Backend (Python 3.12/FastAPI):
- 5 models: Transaction, DetectionRule, FraudAlert, AuditLog, RuleSnapshot
- Rule engine: 4 rule types (amount, location, time, pattern)
- 11 API routes: health, auth, transactions, alerts
- Sync ingestion pipeline with explanation generation
- JWT auth with 3 roles (analyst, admin, senior)
- Seed script with 5 default rules + 50 synthetic transactions

Frontend (React 19/TypeScript/Tailwind):
- Auth: login page, JWT token management, role-based routing
- Alerts: queue with filters, detail panel, decision workflow
- Layout: responsive sidebar, top bar, protected routes
- Full TypeScript, zero ts-ignore, Tailwind CSS

Build: Backend imports clean, Frontend tsc --noEmit passes,
vite build produces 296KB production bundle.

frontend/src/pages/AlertsPage.tsx

@@ -0,0 +1,18 @@
+import { useState } from 'react';
+import AlertQueue from '../components/alerts/AlertQueue';
+import AlertDetailPanel from '../components/alerts/AlertDetail';
+
+export default function AlertsPage() {
+  const [selectedId, setSelectedId] = useState<string | null>(null);
+
+  return (
+    <div className="flex h-full">
+      <div className="w-2/5 border-r bg-white overflow-hidden">
+        <AlertQueue selectedId={selectedId} onSelect={setSelectedId} />
+      </div>
+      <div className="w-3/5 overflow-hidden">
+        <AlertDetailPanel alertId={selectedId} />
+      </div>
+    </div>
+  );
+}