feat(frontend): opt-in Other Models toggles, hidden nav and announcement

- The Other nav entry is hidden while the feature is off
  (nav-item--hidden, toggled client-side after enabling) and now uses the
  fa-shapes icon.
- Shared utils/otherModels.js helpers (enable through the settings API,
  open the settings Library section) are reused by the disabled page, the
  announcement banner and the download modal.
- BannerService registers a one-time dismissible "other-models-announcement"
  banner while the feature is off; SettingsManager drops the banner and
  updates the nav when the master switch flips.
- A disabled download routing answer now surfaces a showActionToast with an
  "Enable Other Models" action.
- Settings UI: master toggle + five sub_type checkboxes whose default-root
  selects are disabled when unchecked; i18n keys added to en.json and synced
  (other locales keep TODO placeholders).

static/js/state/index.js

@@ -25,6 +25,8 @@ const DEFAULT_SETTINGS_BASE = Object.freeze({
     default_checkpoint_root: '',
     default_embedding_root: '',
     default_other_roots: {},
+    enable_other_models: false,
+    enabled_other_sub_types: ['vae', 'upscaler', 'text_encoder', 'clip_vision'],
     recipes_path: '',
     base_model_path_mappings: {},
     download_path_templates: {},
@@ -74,6 +76,7 @@ export function createDefaultSettings() {
         download_path_templates: { ...DEFAULT_PATH_TEMPLATES },
         priority_tags: { ...DEFAULT_PRIORITY_TAG_CONFIG },
         default_other_roots: {},
+        enabled_other_sub_types: ['vae', 'upscaler', 'text_encoder', 'clip_vision'],
     };
 }