fix(gui): Final Phase 7 stabilization and polish

- Resolve ImportError by correctly prefixing 'src' in modular renderers.
- Fix ImGui access violation by ensuring push_id always receives string IDs.
- Restore visible role-based background tints using layered rendering (channels).
- Definitively fix horizontal Markdown table widths by forcing group expansion.
- Centralize color management in theme_2.py and ui_shared.py.
- Standardize Files & Media inventory layout and remove legacy controls.
- Update test mocks to support modular UI and theme-driven styling.

tests/test_gui_symbol_navigation.py

@@ -11,7 +11,11 @@ def test_render_discussion_panel_symbol_lookup(mock_app, role):
   patch('src.gui_2.imscope') as mock_imscope,
   patch('src.gui_2.mcp_client') as mock_mcp,
   patch('src.gui_2.project_manager') as mock_pm,
-  patch('src.markdown_helper.imgui_md') as mock_md
+  patch('src.markdown_helper.imgui_md') as mock_md,
+  patch('src.ui_shared.imgui', mock_imgui),
+  patch('src.ui_shared.imscope', mock_imscope),
+  patch('src.theme_2.imgui', mock_imgui),
+  patch('src.theme_2.imscope', mock_imscope)
  ):
   # Setup imscope mocks
   mock_imscope.window.return_value.__enter__.return_value = (True, True)