fix(gui): Resolve Text Viewer docking conflict with unified ID

- Update Text Viewer window ID to '###Text_Viewer_Unified'.
- Ensures ImGui treats the window as a single stable entity across title changes.
- Prevents docking loop glitches.

tests/test_gui_text_viewer_docking.py

@@ -25,7 +25,7 @@ def test_text_viewer_window_id_stability():
   # Verify imgui.begin was called with the stable ID suffix
   args, _ = mock_imgui.begin.call_args
   window_title = args[0]
-  assert "###Text_Viewer_Stable" in window_title
+  assert "###Text_Viewer_Unified" in window_title
   assert window_title.startswith("Custom Title")
 
 def test_text_viewer_window_default_title_id_stability():
@@ -50,5 +50,5 @@ def test_text_viewer_window_default_title_id_stability():
   # Verify imgui.begin was called with the stable ID suffix
   args, _ = mock_imgui.begin.call_args
   window_title = args[0]
-  assert "###Text_Viewer_Stable" in window_title
+  assert "###Text_Viewer_Unified" in window_title
   assert window_title.startswith("Text Viewer")