fix: Prisma 7 adapter-based connection (no url in schema)

- Use @prisma/adapter-pg for PrismaClient (Prisma 7 removed datasourceUrl/datasources)
- prisma.config.ts: migrate.url for CLI commands
- schema.prisma: no url in datasource (Prisma 7 requirement)

package.json

@@ -18,6 +18,7 @@
   "dependencies": {
     "@livekit/components-react": "^2.9.20",
     "@livekit/components-styles": "^1.2.0",
+    "@prisma/adapter-pg": "^7.5.0",
     "@prisma/client": "^7.5.0",
     "@tailwindcss/postcss": "^4.2.2",
     "@types/node": "^25.5.0",
@@ -29,6 +30,7 @@
     "livekit-client": "^2.17.3",
     "livekit-server-sdk": "^2.15.0",
     "next": "^16.2.1",
+    "pg": "^8.20.0",
     "postcss": "^8.5.8",
     "prisma": "^7.5.0",
     "react": "^19.2.4",