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

static/js/state/index.js

@@ -77,6 +77,12 @@ export function createDefaultSettings() {
         priority_tags: { ...DEFAULT_PRIORITY_TAG_CONFIG },
         default_other_roots: {},
         enabled_other_sub_types: ['vae', 'upscaler', 'text_encoder'],
+        // Standalone-only fields populated by GET /api/lm/settings; in plugin
+        // mode the backend omits folder_paths/folder_path_schema and these
+        // defaults apply.
+        standalone_mode: false,
+        folder_paths: {},
+        folder_path_schema: [],
     };
 }