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/api/drizzle.config.ts

@@ -0,0 +1,15 @@
+// Source: https://orm.drizzle.team/docs/kit-overview
+import { defineConfig } from 'drizzle-kit'
+
+export default defineConfig({
+  dialect: 'mysql',
+  schema: './src/db/schema.ts',
+  out: './src/db/migrations',
+  dbCredentials: {
+    host: process.env.DB_HOST!,
+    user: process.env.DB_USER!,
+    password: process.env.DB_PASSWORD!,
+    database: process.env.DB_NAME!,
+    port: Number(process.env.DB_PORT ?? 3306),
+  },
+})