Backend now returns { code: ErrorCode, message: string } for all errors,
making it language-agnostic. Frontend maps codes to localised strings via
Paraglide (en/de/es), so translations live in messages/*.json.
- Add ErrorCode enum and DomainException with static factory methods
- Update GlobalExceptionHandler to return ErrorResponse(code, message)
- Replace ResponseStatusException throughout controllers/services/aspects
- Add frontend errors.ts with parseBackendError() and getErrorMessage()
- getErrorMessage() delegates to Paraglide m.error_*() functions
- Add error_* keys to messages/en.json, de.json, es.json
- Update all page.server.ts files to use the new error utilities
- Fix hardcoded localhost URLs in admin and login pages
- Fix missing baseUrl in deleteTag action
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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