feat(other-models): announce the feature only when folders are available

Other Models management is opt-in and its folders come from
folder_paths.get_folder_paths(). In plugin mode ComfyUI registers vae,
upscale_models, text_encoders, clip_vision and controlnet out of the box, so
enabling the feature works immediately. Standalone only knows the keys present
in settings.json.folder_paths, and that file is edited by hand - there is no UI
for those keys - so a standalone user who followed the announcement banner
reached "Enable Other Models" and then an empty page.

Gate the announcement on the capability instead of on how the process was
started:

- Config.get_other_models_availability() probes every canonical other key
  (legacy clip collapses into text_encoders where the host exposes
  map_legacy) and reports which sub_types resolve to a folder that exists on
  disk. It deliberately ignores enable_other_models: the question is "could
  this work here at all?". An empty folder counts, because CivitAI downloads
  can target it.
- /api/lm/settings exposes it as the derived, non-persisted
  other_models_paths_available flag; a probe failure yields null and the
  banner fails open.
- BannerService only registers the announcement when the flag is not false.
  `=== false` (not falsy) keeps a cached/older payload working, and nothing is
  written to dismissed_banners, so the banner can return once folders exist.
- The Other page grows an "enabled but nothing to scan" empty state driven by
  config.other_roots, showing the settings.json snippet for standalone and a
  pointer to ComfyUI model paths otherwise, plus an Open Settings action. It
  also covers the corner where only a non-default sub_type has a folder.

Translate the six other.noPaths.* keys into all nine locales and record the
new "folder key" / "on disk" terminology in the i18n guidelines.

Backend tests and pytest tests/i18n could not run in this environment (no
pytest/platformdirs); the probe was exercised against a stubbed folder_paths.
Frontend: 120 files / 1101 JS tests passed.

tests/frontend/managers/BannerService.test.js

@@ -214,6 +214,7 @@ describe('BannerService', () => {
 
         beforeEach(() => {
             state.global.settings.enable_other_models = false;
+            state.global.settings.other_models_paths_available = true;
         });
 
         it('announces the feature while it is switched off', () => {
@@ -225,6 +226,25 @@ describe('BannerService', () => {
                 .toContain('Other Models Management is available');
         });
 
+        it('stays silent when the host exposes no other-model folders', () => {
+            // Standalone installs without the folder_paths keys in
+            // settings.json would land on an empty page, so do not announce.
+            state.global.settings.other_models_paths_available = false;
+
+            prepareBanner();
+
+            expect(bannerElement()).toBeNull();
+            expect(bannerService.banners.has(OTHER_MODELS_BANNER_ID)).toBe(false);
+        });
+
+        it('still announces when availability is unknown (older payload)', () => {
+            delete state.global.settings.other_models_paths_available;
+
+            prepareBanner();
+
+            expect(bannerElement()).not.toBeNull();
+        });
+
         it('stays silent once the feature is enabled', () => {
             state.global.settings.enable_other_models = true;