feat(metadata): add CivArchive API toggle and provider fallback order settings

- Add enable_civarchive_api toggle (default on) to allow disabling
  CivArchive to avoid its rate-limit windows entirely
- Add metadata_provider_order dropdown with two presets:
  CivitAI → CivArchive → Archive DB (default) and
  CivitAI → Archive DB → CivArchive
- Wire both settings through backend (metadata_service, settings_manager,
  misc_handlers) and frontend (SettingsManager, state, settings modal)
- Reorder Metadata section in settings modal: toggles → status/management
  → fallback order, for natural top-down workflow
- Make update_metadata_providers() log the effective provider chain
  using actually-registered providers rather than settings assumptions
- Add 5 test cases covering all provider-combination paths
- Complete i18n translations for 6 new keys across all 9 non-English locales

py/services/settings_manager.py

@@ -65,6 +65,8 @@ DEFAULT_SETTINGS: Dict[str, Any] = {
     "onboarding_completed": False,
     "dismissed_banners": [],
     "enable_metadata_archive_db": False,
+    "enable_civarchive_api": True,
+    "metadata_provider_order": "civitai_archive_sqlite",
     "proxy_enabled": False,
     "proxy_host": "",
     "proxy_port": "",