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.

py/routes/handlers/misc_handlers.py

@@ -1559,6 +1559,22 @@ class SettingsHandler:
             response_data["civitai_api_key_set"] = bool(raw_key)
             raw_llm_key = self._settings.get("llm_api_key")
             response_data["llm_api_key_set"] = bool(raw_llm_key)
+            # Derived capability flag (not persisted): whether the host exposes
+            # any other-model folder at all. Standalone installs only know the
+            # folder_paths keys present in settings.json, so the announcement
+            # banner uses this to avoid promising a page that cannot list
+            # anything.
+            try:
+                availability = config.get_other_models_availability()
+                response_data["other_models_paths_available"] = bool(
+                    availability.get("available")
+                )
+            except Exception as availability_error:  # pragma: no cover - defensive
+                logger.debug(
+                    "Could not resolve Other Models availability: %s",
+                    availability_error,
+                )
+                response_data["other_models_paths_available"] = None
             settings_file = getattr(self._settings, "settings_file", None)
             if settings_file:
                 response_data["settings_file"] = settings_file