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

tests/test_standalone_settings.py

@@ -52,12 +52,18 @@ def test_missing_settings_creates_defaults_and_emits_warnings(tmp_path):
 
     actions = warning.get("actions") or []
     assert actions == [
+        {
+            "action": "open-model-paths-settings",
+            "label": "Configure model folders",
+            "type": "primary",
+            "icon": "fas fa-cog",
+        },
         {
             "action": "open-settings-location",
             "label": "Open settings folder",
             "type": "primary",
             "icon": "fas fa-folder-open",
-        }
+        },
     ]
 
 
@@ -155,3 +161,13 @@ def test_apply_settings_dir_from_argv():
             os.environ.pop("LORA_MANAGER_SETTINGS_DIR", None)
         else:
             os.environ["LORA_MANAGER_SETTINGS_DIR"] = previous
+
+
+def test_template_folder_path_placeholders_are_exposed():
+    manager = get_settings_manager()
+
+    placeholders = manager.get_template_folder_path_placeholders()
+
+    assert "C:/path/to/your/loras_folder" in placeholders
+    assert "C:/path/to/another/embeddings_folder" in placeholders
+    assert len(placeholders) == 8