Centralize Win32 app runtime binding setup

docs/modernization/roadmap.md

@@ -97,6 +97,10 @@ Latest slice:
   and bound-tablet bindings beside the retained owned `App`, `AppRuntime*`,
   and `WacomTablet` objects instead of leaving that binding surface in
   `windows_runtime_shell.cpp`.
+- `src/platform_windows/windows_runtime_state.*` now also owns the Win32
+  owned-app creation plus app/runtime binding handoff, so
+  `windows_runtime_shell.cpp` is down to a thinner startup dispatcher over the
+  retained runtime-state helper.
 - `src/platform_windows/windows_runtime_shell.h` is now a thinner runtime
   entrypoint header that picks up the retained binding surface from
   `windows_runtime_state.h` instead of declaring a second shell-owned binding