feat(api): scaffold Fastify server with health route

- ESM Fastify 4 with Pino logger (pretty-print in dev only)
- Plugins: helmet, cors (allowlist via CORS_ORIGINS), rate-limit, sensible
- Zod-validated environment config in src/config/env.ts
- Modular structure under src/modules with /health route
- tsx watch for dev, tsc for build, dist/server.js as production entry

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/api/src/modules/health/health.routes.ts

@@ -0,0 +1,9 @@
+import type { FastifyPluginAsync } from 'fastify';
+
+export const healthRoutes: FastifyPluginAsync = async (fastify) => {
+  fastify.get('/health', async () => ({
+    status: 'ok',
+    uptime: process.uptime(),
+    timestamp: new Date().toISOString(),
+  }));
+};