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

docker-compose.yml

@@ -17,6 +17,11 @@ services:
       - PRO_KEYS=${PRO_KEYS}
       - SMTP_HOST=host.docker.internal
       - SMTP_PORT=25
+      - DATABASE_HOST=172.17.0.1
+      - DATABASE_PORT=5432
+      - DATABASE_NAME=docfast
+      - DATABASE_USER=docfast
+      - DATABASE_PASSWORD=${DATABASE_PASSWORD:-docfast}
       - POOL_SIZE=15
       - BROWSER_COUNT=1
       - PAGES_PER_BROWSER=15