feat(auth): remove username field, migrate identity to email
- AppUser entity: replace username with email (NOT NULL, UNIQUE,
colon-pattern validated)
- AppUserRepository: remove findByUsername, rename search JPQL to
searchByEmailOrName (searches email + firstName + lastName)
- CreateUserRequest: remove username, require email with colon guard
- UserService: rename findByUsername→findByEmail, createUserOrUpdate
upserts by email, blank-email guard throws instead of setting null
- UserController + all other controllers: findByEmail(auth.getName())
- DataInitializer: email-based config and lookup, E2E users have email
- V44 migration: pre-check + email NOT NULL + drop username column
- All tests updated: .username() builders removed, mocks updated,
NotificationRepositoryTest fixtures include email fields
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
e8039bca5a