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

static/js/state/index.js

@@ -13,6 +13,8 @@ const DEFAULT_SETTINGS_BASE = Object.freeze({
     language: 'en',
     show_only_sfw: false,
     enable_metadata_archive_db: false,
+    enable_civarchive_api: true,
+    metadata_provider_order: 'civitai_archive_sqlite',
     proxy_enabled: false,
     proxy_type: 'http',
     proxy_host: '',