FRE-4493: Implement API gateway with rate limiting and routing

- Add Fastify-based API server entry point
- Implement tier-based rate limiting middleware (basic/plus/premium)
- Add authentication middleware (JWT + API key support)
- Create error handling middleware with standardized responses
- Add request/response logging with request IDs
- Configure CORS and security headers
- Implement API route structure with health check and service discovery
- Set up API versioning configuration

Files: apps/api/src/{index.ts,middleware/*.ts,routes/index.ts}

apps/api/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "api",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "tsx watch src/index.ts",
+    "build": "tsc",
+    "lint": "eslint src/"
+  },
+  "dependencies": {
+    "@fastify/cors": "^11.2.0",
+    "@fastify/helmet": "^13.0.2",
+    "@shieldsai/shared-auth": "*",
+    "@shieldsai/shared-db": "*",
+    "@shieldsai/shared-utils": "*",
+    "fastify": "^4.25.0",
+    "fastify-plugin": "^4.5.0"
+  },
+  "devDependencies": {
+    "@types/node": "^25.6.0",
+    "tsx": "^4.7.1",
+    "typescript": "^5.3.3"
+  }
+}