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

selective-vpn-gui/main_window/singbox_mixin.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from main_window.singbox import (
+    SingBoxCardsMixin,
+    SingBoxEditorMixin,
+    SingBoxLinksMixin,
+    SingBoxRuntimeMixin,
+)
+
+
+class SingBoxMainWindowMixin(
+    SingBoxRuntimeMixin,
+    SingBoxLinksMixin,
+    SingBoxCardsMixin,
+    SingBoxEditorMixin,
+):
+    """Facade mixin for backward-compatible MainWindow inheritance."""
+
+
+__all__ = ["SingBoxMainWindowMixin"]