Extract UI state and Win32 window shell

docs/modernization/tasks.md

@@ -153,6 +153,11 @@ Current slice:
   `legacy_node_stroke_preview_execution_services.h`, which trims another
   coherent pass-setup block from `src/node_stroke_preview.cpp`, but broader
   preview-pass orchestration is still inline.
+- `NodeStrokePreview::draw_stroke_immediate()` immediate preview pass
+  sequencing now also routes through the private
+  `execute_stroke_draw_immediate_pass_sequence(...)` helper, which removes
+  another live orchestration block from the node even though worker/readback
+  flow still remains in the file.
 - `NodeCanvas` merged-path per-plane merged-texture draw execution now also
   routes through `execute_legacy_canvas_draw_merge_layer_texture(...)`.
 - `NodeCanvas` merged-path and non-blend checkerboard background setup now also
@@ -298,7 +303,7 @@ targets look like helpers under one old monolith.
 Status: In Progress
 
 Why now:
-`src/app_layout.cpp` is still a 717-line mixed file that builds menus,
+`src/app_layout.cpp` is still a 353-line mixed file that builds menus,
 attaches callbacks, computes planner inputs, and mutates UI state directly.
 
 Current slice:
@@ -325,6 +330,9 @@ Current slice:
   `App::init_menu_edit()` is now a thin call-through, but draw-toolbar,
   brush-refresh, and broader layout composition are still inline in
   `src/app_layout.cpp`.
+- UI-direction plus persisted floating/docked panel-state ownership now also
+  lives in `src/app_layout_ui_state.cpp`, and `src/app_layout.cpp` is down to
+  the remaining draw-toolbar, brush-refresh, and layout/bootstrap composition.
 
 Write scope:
 - `src/app_layout.cpp`
@@ -489,8 +497,11 @@ Current slice:
   `src/platform_windows/windows_bootstrap_helpers.*` for runtime-data
   discovery, startup-state initialization, window creation, pixel-format
   setup, GL loader init, runtime-info logging, and core-context upgrade
-  sequencing, which materially thins `src/main.cpp`, but the retained Win32
-  window procedure and broader shell flow are still open
+  sequencing
+- the Win32 window procedure and retained message-handling shell now also live
+  in `src/platform_windows/windows_window_shell.*` instead of `src/main.cpp`,
+  which materially thins the entry file even though broader runtime/entrypoint
+  composition is still open
 - prepared-file background work now runs through an `AppRuntime`-owned worker
   queue instead of a retained static worker in `src/app_events.cpp`
 - canvas async import/export/save/open background work now also runs through an