feat(settings): editable model library paths for standalone mode

Standalone users previously had to hand-edit settings.json to configure
primary folder_paths. Add a standalone-only Model Paths section to the
settings modal:

- Backend exposes standalone_mode, folder_paths (with template placeholder
  values filtered out) and a data-driven folder_path_schema derived from
  OTHER_MODEL_FOLDER_SUBTYPES via GET /api/lm/settings
- The new section renders multi-path editors per model type from the
  schema, with inline enable_other_models / sub-type controls so other
  model types are configured without leaving the tab
- Persistent restart-required cues after a save: nav dot, inline notice
  and a global banner (unique id per change so dismissals don't mute
  future reminders)
- The missing-model-paths startup banner and the Other Models no-paths
  empty state now deep-link into the new section instead of pointing at
  settings.json

AGENTS.md

@@ -192,6 +192,15 @@ The system runs in two modes:
 - Auto-saves paths to `settings.json` in ComfyUI mode
 - `settings.json.example` is intentionally minimal (see Important Notes); all
   other defaults live in `DEFAULT_SETTINGS` (`py/services/settings_manager.py`)
+- **`folder_paths` vs `extra_folder_paths` — different purposes, do not conflate:**
+  - `folder_paths` (primary model roots): in ComfyUI plugin mode these come
+    from the ComfyUI host; in standalone mode they are the ONLY source of
+    model library paths and are currently edited by hand in `settings.json`.
+  - `extra_folder_paths` is a **ComfyUI-plugin-mode feature**: paths visible
+    ONLY to LoRA Manager, not to ComfyUI. Its motivation is that a very large
+    model library slows ComfyUI itself down, while LoRA Manager handles large
+    libraries without performance issues — so users keep ComfyUI's library
+    small and add the bulk via `extra_folder_paths`.
 
 ### Frontend UI Architecture