#696 Test

Summary by cubic

Adds an optional account_id override to DELETE /api/artists/{id} so authorized org members or admins can delete an artist under another account’s context. The override is validated as a UUID and passed into validateAuthContext; invalid input returns 400.

• New Features
  • Parse JSON body with safeParseJson and validate with zod (account_id optional UUID); return 400 on malformed JSON or invalid UUID.
  • Pass { accountId } to validateAuthContext and enforce access with checkAccountArtistAccess.
  • Tests updated to cover override flow, invalid account_id, and default behavior ({ accountId: undefined }).