refactor: remove legacy source compatibility code

[onmax]

Summary

• remove deprecated auth.database.provider guard in module setup
• remove schema-generator compatibility cast workaround
• add test coverage to verify legacy provider option is ignored during module boot

Validation

• pnpm test (fails)
  • failure caused by removing schema-generator compatibility workaround
  • reported errors include TS2740 and TS2322 in src/schema-generator.ts
• remaining checks (pnpm typecheck, pnpm typecheck:runtime-server, pnpm -C /Users/maxi/nuxt/saas typecheck) not run after stop-on-failure rule

Related

• defineServerAuth widens literal types despite const generic #134
• typed nitro route inference for /api/auth endpoints #194

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@onmax/nuxt-better-auth@243

commit: 145de52