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/utils/otherModels.js

@@ -50,3 +50,19 @@ export function openOtherModelsSettings() {
         });
     }, 100);
 }
+
+/**
+ * Open the settings modal on the standalone-only Model Paths section, where
+ * primary folder_paths are edited. The section only exists in standalone mode,
+ * so the nav item lookup simply no-ops elsewhere.
+ */
+export function openModelPathsSettings() {
+    const modalManager = window.modalManager;
+    if (modalManager && typeof modalManager.showModal === 'function') {
+        modalManager.showModal('settingsModal');
+    }
+
+    window.setTimeout(() => {
+        document.querySelector('.settings-nav-item[data-section="modelPaths"]')?.click();
+    }, 100);
+}