fix: prisma url in schema + first user becomes ADMIN

- Add url = env("DATABASE_URL") back to schema (required by Prisma 7.5)
- Simplify prisma.config.ts
- First registered user auto-promoted to ADMIN via databaseHooks
- Subsequent users get HOST role

CLAUDE.md

@@ -173,8 +173,8 @@ DEV_ACCESS_KEY=mySecretKey123
 ## Prisma 7 Notes
 
 - `prisma.config.ts` in project root (required by Prisma 7)
-- `datasourceUrl` passed via PrismaClient constructor, not in schema
-- Schema has no `url` in datasource block — only `provider`
+- `url = env("DATABASE_URL")` in schema datasource — standard approach, works with CLI and PrismaClient
+- `new PrismaClient()` without arguments — URL resolved from schema's `env("DATABASE_URL")`
 - Use `-- --webpack` flag for `next build` on Windows (Turbopack WASM issue)
 
 ## Auth Notes