Migrate from JSON to PostgreSQL, update SLA to 99.5%

- Replace JSON file storage with PostgreSQL (pg package)
- Add db.ts service for connection pool and schema init
- Rewrite keys.ts, verification.ts, usage.ts for async PostgreSQL
- Update all routes for async function signatures
- Add migration script (scripts/migrate-to-postgres.mjs)
- Update docker-compose.yml with DATABASE_* env vars
- Change SLA from 99.9% to 99.5% in landing page

package.json

@@ -18,7 +18,8 @@
     "nodemailer": "^8.0.1",
     "puppeteer": "^24.0.0",
     "stripe": "^20.3.1",
-    "swagger-ui-dist": "^5.31.0"
+    "swagger-ui-dist": "^5.31.0",
+    "pg": "^8.13.0"
   },
   "devDependencies": {
     "@types/express": "^5.0.0",
@@ -26,7 +27,8 @@
     "@types/nodemailer": "^7.0.9",
     "tsx": "^4.19.0",
     "typescript": "^5.7.0",
-    "vitest": "^3.0.0"
+    "vitest": "^3.0.0",
+    "@types/pg": "^8.11.0"
   },
   "type": "module"
-}
+}