platform: modularize api/gui, add docs-tests-web foundation, and refresh root config

selective-vpn-gui/main_window/ui_tabs_mixin.py

@@ -0,0 +1,16 @@
+from __future__ import annotations
+
+from main_window.ui_tabs_main_mixin import UITabsMainMixin
+from main_window.ui_tabs_other_mixin import UITabsOtherMixin
+from main_window.ui_tabs_singbox_mixin import UITabsSingBoxMixin
+
+
+class UITabsMixin(
+    UITabsOtherMixin,
+    UITabsSingBoxMixin,
+    UITabsMainMixin,
+):
+    """Facade mixin for MainWindow tab builders."""
+
+
+__all__ = ["UITabsMixin"]