Move Win32 async context ownership and trim canvas draw setup

docs/modernization/roadmap.md

@@ -117,9 +117,9 @@ Current architecture mismatches that must be treated as real blockers:
   checkerboard background setup now route through retained draw-merge helpers,
   with the cache-to-screen checkerboard-plane callback setup also reduced and
   the merged-path checkerboard background-plane callback plus per-plane
-  merged-texture draw plus the smoothing-mask face shader/draw pass plus
-  heightmap, current-mode, and grid-mode callback setup now routed through the
-  same retained helper family.
+  merged-texture draw callback plus the smoothing-mask face shader/draw pass
+  plus heightmap, current-mode, and grid-mode callback setup now routed
+  through the same retained helper family.
 - `app_layout.cpp` and `app_dialogs.cpp` are still mixed shell/controller files
   rather than thin composition/binding surfaces.
 - `App`, `Canvas`, `Node`, retained workers, and platform entrypoints still use
@@ -135,13 +135,15 @@ Current architecture mismatches that must be treated as real blockers:
   coordination flags now use `std::atomic` instead of unsynchronized globals,
   while the main Win32 entrypoint now groups window/GL/task/VR state behind a
   retained local state object instead of separate process-wide globals, the
-  canvas async worker now sits behind a named retained local worker-state
-  helper instead of a bare static accessor, the prepared-file worker and the
-  canvas async import/export/save/open worker now live under `AppRuntime`
-  instead of retained static app-events/canvas workers, and `App::rec_loop()`
-  now delegates worker-iteration orchestration into the retained recording
-  bridge even though that retained recording path still owns the worker-side
-  readback flow.
+  Win32 async GL/context lock state now lives under
+  `src/platform_windows/windows_platform_services.cpp` instead of `main.cpp`
+  retained state, the canvas async worker now sits behind a named retained
+  local worker-state helper instead of a bare static accessor, the
+  prepared-file worker and the canvas async import/export/save/open worker now
+  live under `AppRuntime` instead of retained static app-events/canvas
+  workers, and `App::rec_loop()` now delegates worker-iteration orchestration
+  into the retained recording bridge even though that retained recording path
+  still owns the worker-side readback flow.
 - Modern C++23 usage exists in extracted components, especially `std::span`,
   explicit result/status objects, and a few concepts, but the live app still
   does not consistently express ownership, thread affinity, or renderer