test: verify Next.js application works with PostgreSQL

- Updated .env to use DATABASE_URL instead of DATABASE_PATH
- Tested all API endpoints: health, charts, candles, span annotations
- Confirmed JSONB fields work correctly (geometry, sub_spans, model_prediction)
- All 2,836 rows accessible via API
- Database connection pooling working correctly

next-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/types/routes.d.ts";
+import "./.next/dev/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.