feat(01-01): Drizzle schema + DB client + /health slice (GREEN)

- src/db/schema.ts: users, memberCredentials, calendars, calendarEvents tables
  - users: composite unique on oidc_iss+oidc_sub (D-10 identity)
  - calendar_events: separate dtstart_utc (TIMESTAMP) and dtstart_date (DATE) + allDay boolean (D-13)
- src/db/client.ts: drizzle(mysql2 pool) singleton export `db`
- drizzle.config.ts: dialect mysql, schema → migrations, dbCredentials from env
- src/routes/health.ts: GET / with real SELECT 1 DB round-trip, 200 or 503
- src/index.ts: Hono app with /health mounted before auth, serveStatic for PWA
- tests/health.test.ts: 2 tests pass (mocked DB); TDD GREEN gate
- apps/pwa/src/App.tsx: React shell fetching /health via TanStack Query

apps/pwa/src/App.tsx

@@ -0,0 +1,41 @@
+import { useQuery } from '@tanstack/react-query'
+
+interface HealthResponse {
+  ok: boolean
+  db: string
+}
+
+async function fetchHealth(): Promise<HealthResponse> {
+  const res = await fetch('/health')
+  if (!res.ok) {
+    throw new Error(`Health check failed: ${res.status}`)
+  }
+  return res.json() as Promise<HealthResponse>
+}
+
+export default function App() {
+  const { data, isLoading, isError } = useQuery({
+    queryKey: ['health'],
+    queryFn: fetchHealth,
+    retry: 1,
+    refetchInterval: 30_000,
+  })
+
+  return (
+    <div style={{ fontFamily: 'system-ui, sans-serif', padding: '2rem', maxWidth: '480px', margin: '0 auto' }}>
+      <h1 style={{ fontSize: '1.5rem', marginBottom: '1rem' }}>FamilySync</h1>
+      <div
+        style={{
+          padding: '1rem',
+          borderRadius: '8px',
+          background: isLoading ? '#f5f5f5' : isError ? '#fee2e2' : '#dcfce7',
+          color: isLoading ? '#666' : isError ? '#991b1b' : '#166534',
+        }}
+      >
+        {isLoading && 'Checking stack...'}
+        {isError && 'stack: down'}
+        {data && `stack: ${data.ok && data.db === 'up' ? 'up' : 'down'}`}
+      </div>
+    </div>
+  )
+}