fix: migrate to Prisma 7 driver adapter (libsql) for SQLite

Prisma 7 removed support for `url` in schema.prisma datasources and the
`engineType = "library"` native binary engine. All connections now go
through a driver adapter.

- Remove engineType and url from schema.prisma (no longer supported)
- Configure prisma.config.ts with migrate.adapter using @libsql/client
- Instantiate PrismaClient with PrismaLibSQL adapter in src/lib/prisma.ts
- Add @libsql/client and @prisma/adapter-libsql dependencies
- Remove PRISMA_CLIENT_ENGINE_TYPE from Dockerfile (obsolete)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -9,7 +9,9 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@libsql/client": "^0.14.0",
     "@next-auth/prisma-adapter": "^1.0.7",
+    "@prisma/adapter-libsql": "^7.5.0",
     "@prisma/client": "^7.5.0",
     "googleapis": "^171.4.0",
     "lucide-react": "^0.577.0",