test(rag): Fix test_rag_gui_presence.py source inspection targets

Updated tests to inspect _render_ai_settings_hub instead of _gui_func as the RAG settings panel was moved during GUI refactoring.

tests/test_rag_gui_presence.py

@@ -8,8 +8,8 @@ def test_rag_panel_exists():
  assert callable(App._render_rag_panel)
 
 def test_rag_panel_integration():
- """Verify that _gui_func calls _render_rag_panel by inspecting source or via mock."""
+ """Verify that _render_ai_settings_hub calls _render_rag_panel by inspecting source or via mock."""
  import inspect
- source = inspect.getsource(App._gui_func)
+ source = inspect.getsource(App._render_ai_settings_hub)
  assert "self._render_rag_panel()" in source
  assert "imgui.collapsing_header(\"RAG Settings\")" in source