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/package.json

@@ -0,0 +1,29 @@
+{
+  "name": "@ketopath/api",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "tsx watch src/server.ts",
+    "build": "tsc",
+    "start": "node dist/server.js",
+    "typecheck": "tsc --noEmit",
+    "lint": "eslint src --max-warnings=0"
+  },
+  "dependencies": {
+    "@fastify/cors": "^9.0.1",
+    "@fastify/helmet": "^11.1.1",
+    "@fastify/rate-limit": "^9.1.0",
+    "@fastify/sensible": "^5.6.0",
+    "@ketopath/shared": "workspace:*",
+    "fastify": "^4.28.1",
+    "zod": "^3.23.8"
+  },
+  "devDependencies": {
+    "@ketopath/eslint-config": "workspace:*",
+    "@ketopath/tsconfig": "workspace:*",
+    "@types/node": "^20.12.7",
+    "pino-pretty": "^11.2.1",
+    "tsx": "^4.16.2"
+  }
+}