chore(db): migrate from SQLite to PostgreSQL

- Change Prisma provider from sqlite to postgresql
- Replace better-sqlite3 adapter with @prisma/adapter-pg
- Update prisma.config.ts and lib/prisma.ts for PostgreSQL
- Add DATABASE_URL to .env.local
- Regenerate Prisma client for PostgreSQL
- Recreate migrations for PostgreSQL database

lib/generated/prisma/models/DailyPuzzle.ts

@@ -1094,6 +1094,7 @@ export type DailyPuzzleCreateManyArgs<ExtArgs extends runtime.Types.Extensions.I
    * The data used to create many DailyPuzzles.
    */
   data: Prisma.DailyPuzzleCreateManyInput | Prisma.DailyPuzzleCreateManyInput[]
+  skipDuplicates?: boolean
 }
 
 /**
@@ -1112,6 +1113,7 @@ export type DailyPuzzleCreateManyAndReturnArgs<ExtArgs extends runtime.Types.Ext
    * The data used to create many DailyPuzzles.
    */
   data: Prisma.DailyPuzzleCreateManyInput | Prisma.DailyPuzzleCreateManyInput[]
+  skipDuplicates?: boolean
 }
 
 /**