feat(other): guide standalone users to settings.json from the no-paths empty state

The standalone empty state showed the folder_paths keys but not where to
put them, and its Open Settings button led to a modal that cannot edit
primary folder paths. Now the page shows the real settings.json path and
an Open Settings Folder button backed by the existing open-location API.

Also stop open_settings_location from claiming success on headless Linux
sessions: with no DISPLAY/WAYLAND_DISPLAY, xdg-open cannot work, so the
handler now returns clipboard mode and the browser copies/shows the path
instead.

locales/ja.json

@@ -1245,7 +1245,8 @@
             "hintStandalone": "スキャンされるのは上記のフォルダーキーのみです。不要なキーは省略できます。",
             "descriptionComfyUI": "その他のモデル管理はオンですが、設定されたモデルフォルダーがディスク上に存在しません。該当するモデルフォルダーをComfyUIのモデルパスに追加し、このページを再読み込みしてください。",
             "hintComfyUI": "その他のモデルは、ComfyUIのvae、upscale_models、text_encoders、clip_vision、controlnetフォルダーから読み込まれます。",
-            "openSettings": "設定を開く"
+            "openSettings": "設定を開く",
+            "openSettingsFolder": "[TODO: Translate] Open Settings Folder"
         }
     },
     "sidebar": {