Fix backend API parity: document filters, task days param, i18n locales, contract tests

- Add document list filter support (residence, type, category, contractor, is_active, expiring_soon, search) to handler/service/repo
- Add `days` query param parsing to ListTasks handler (matches ListTasksByResidence)
- Add `error.invalid_token` i18n key to all 9 non-English locale files
- Update contract test to include VerificationResponse mapping

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/i18n/translations/ko.json

@@ -7,6 +7,7 @@
   "error.email_already_taken": "이미 사용 중인 이메일입니다",
   "error.registration_failed": "회원가입에 실패했습니다",
   "error.not_authenticated": "인증되지 않았습니다",
+  "error.invalid_token": "유효하지 않은 토큰입니다",
   "error.failed_to_get_user": "사용자 정보를 가져오는데 실패했습니다",
   "error.failed_to_update_profile": "프로필 업데이트에 실패했습니다",
   "error.invalid_verification_code": "유효하지 않은 인증 코드입니다",