Extract menu, stylus, and canvas draw helpers

docs/modernization/roadmap.md

@@ -80,13 +80,13 @@ What is still carrying too much live ownership:
 Current hotspot files:
 
 - `src/canvas.cpp`: 2645 lines
-- `src/app_layout.cpp`: 1360 lines
+- `src/app_layout.cpp`: 1249 lines
 - `src/canvas_modes.cpp`: 1798 lines
 - `src/node.cpp`: 1551 lines
-- `src/main.cpp`: 1181 lines
+- `src/main.cpp`: 1218 lines
 - `src/node_panel_brush.cpp`: 1197 lines
 - `src/node_stroke_preview.cpp`: 933 lines
-- `src/node_canvas.cpp`: 888 lines
+- `src/node_canvas.cpp`: 968 lines
 - `src/app.cpp`: 950 lines
 - `src/app_dialogs.cpp`: 908 lines
 
@@ -122,14 +122,19 @@ Current architecture mismatches that must be treated as real blockers:
   current-mode, and grid-mode callback setup now routed through the same
   retained helper family, while post-draw callback assembly and the remaining
   per-layer render-path orchestration now also route through retained
-  draw-merge helpers even though the broader node draw loop is still inline.
+  draw-merge helpers even though the broader node draw loop is still inline,
+  with the non-`draw_merged` outer layer/plane traversal now also routing
+  through `execute_legacy_canvas_draw_layer_traversal(...)` while the heavier
+  per-layer GL setup and draw lambdas still live in `src/node_canvas.cpp`.
 - `app_layout.cpp` and `app_dialogs.cpp` are still mixed shell/controller files
   rather than thin composition/binding surfaces, even though tools-menu binding
   plus nested panels/options submenu wiring now live in
   `src/app_layout_tools_menu.cpp` and `App::init_menu_tools()` is now a thin
   call-through, while file-menu binding plus the export submenu wiring now also
   live in `src/app_layout_file_menu.cpp` and `App::init_menu_file()` is now a
-  thin call-through.
+  thin call-through, while about-menu and layer-menu wiring now also live in
+  `src/app_layout_about_layer_menu.cpp` and `App::init_menu_about()` plus
+  `App::init_menu_layer()` are now thin call-throughs.
 - `App`, `Canvas`, `Node`, retained workers, and platform entrypoints still use
   global singleton reach, raw observer pointers, retained static worker
   ownership in several app families, and ad hoc mutex/condition-variable
@@ -153,7 +158,9 @@ Current architecture mismatches that must be treated as real blockers:
   live under `AppRuntime` instead of retained static app-events/canvas
   workers, and the splash-screen dialog loop, HWND ownership, and bitmap setup
   now live in `src/platform_windows/windows_splash.cpp` instead of
-  `src/main.cpp`,
+  `src/main.cpp`, while Win32 pointer API loading, stylus/ink timer decay,
+  Wintab packet reset, and `WM_POINTERUPDATE` pen/touch handling now also live
+  in `src/platform_windows/windows_stylus_input.cpp` instead of `src/main.cpp`,
   while `App::rec_loop()` now delegates worker-iteration orchestration into
   the retained recording bridge, `App::update_rec_frames()` now delegates
   recording label refresh through that same retained recording path, and the