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/routes/test_other_routes.py

@@ -98,17 +98,27 @@ def test_validate_rejects_switched_off_sub_type():
     assert handler._validate_civitai_model_type("Upscaler") is False
 
 
-def test_page_context_reports_feature_state():
+def test_page_context_reports_feature_state(monkeypatch):
+    from py.config import config
     from py.services.settings_manager import get_settings_manager
 
     manager = get_settings_manager()
     handler = OtherRoutes()
     provider = handler._get_page_context_provider()
 
-    assert provider(None) == {"other_disabled": False}
+    monkeypatch.setattr(config, "other_roots", ["/models/vae"], raising=False)
+    context = provider(None)
+    assert context["other_disabled"] is False
+    assert context["other_no_paths"] is False
+
+    # Enabled but nothing resolved: the page must explain how to fix it.
+    monkeypatch.setattr(config, "other_roots", [], raising=False)
+    context = provider(None)
+    assert context["other_disabled"] is False
+    assert context["other_no_paths"] is True
 
     manager.set("enable_other_models", False)
-    assert provider(None) == {"other_disabled": True}
+    assert provider(None) == {"other_disabled": True, "other_no_paths": False}
 
 
 def test_get_expected_model_types_mentions_supported_types():