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/server.ts

@@ -0,0 +1,15 @@
+import { buildApp } from './app.js';
+import { env } from './config/env.js';
+
+async function start(): Promise<void> {
+  const app = await buildApp();
+
+  try {
+    await app.listen({ port: env.PORT, host: env.HOST });
+  } catch (err) {
+    app.log.error(err);
+    process.exit(1);
+  }
+}
+
+void start();