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/css/components/modal/settings-modal.css

@@ -1780,3 +1780,38 @@ input:checked + .toggle-slider:before {
     opacity: 0.5;
     cursor: not-allowed;
 }
+
+/* Standalone Model Paths: pending-restart cues */
+.settings-nav-item.has-pending-restart {
+    position: relative;
+}
+
+.settings-nav-item.has-pending-restart::after {
+    content: '';
+    position: absolute;
+    right: 10px;
+    top: 50%;
+    transform: translateY(-50%);
+    width: 8px;
+    height: 8px;
+    border-radius: 50%;
+    background: var(--lora-warning, #e67e22);
+}
+
+.model-paths-restart-notice {
+    display: none;
+    margin-top: 8px;
+    padding: 10px 14px;
+    border-radius: var(--border-radius-xs);
+    border: 1px solid var(--lora-warning, #e67e22);
+    background: rgba(230, 126, 34, 0.08);
+    color: var(--lora-warning, #e67e22);
+    font-size: 0.85em;
+    line-height: 1.4;
+    align-items: center;
+    gap: 8px;
+}
+
+.model-paths-restart-notice.visible {
+    display: flex;
+}