Extract dialog workflow, bootstrap, and canvas tail helpers

docs/modernization/roadmap.md

@@ -83,12 +83,12 @@ Current hotspot files:
 - `src/app_layout.cpp`: 1249 lines
 - `src/canvas_modes.cpp`: 1798 lines
 - `src/node.cpp`: 1551 lines
-- `src/main.cpp`: 1117 lines
+- `src/main.cpp`: 909 lines
 - `src/node_panel_brush.cpp`: 1197 lines
 - `src/node_stroke_preview.cpp`: 933 lines
-- `src/node_canvas.cpp`: 897 lines
+- `src/node_canvas.cpp`: 905 lines
 - `src/app.cpp`: 502 lines
-- `src/app_dialogs.cpp`: 441 lines
+- `src/app_dialogs.cpp`: 142 lines
 
 Current architecture mismatches that must be treated as real blockers:
 
@@ -128,7 +128,8 @@ Current architecture mismatches that must be treated as real blockers:
   per-layer GL setup now also routes through
   `make_legacy_canvas_draw_merge_layer_path_gl_execution(...)` even though the
   remaining draw lambdas and broader node draw loop still live in
-  `src/node_canvas.cpp`.
+  `src/node_canvas.cpp`, where the post-draw/display-resolve tail now also
+  routes through `execute_node_canvas_draw_merge_tail(...)`.
 - `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
@@ -142,7 +143,9 @@ Current architecture mismatches that must be treated as real blockers:
   and the corresponding `App::dialog_*` entrypoints are thinner, while the
   export/video/PPBR dialog family now also lives in
   `src/app_dialogs_export.cpp` and those `App::dialog_*` entrypoints are
-  thinner too.
+  thinner too, while new/open/save/browse/resize workflow entrypoints now also
+  live in `src/app_dialogs_workflow.cpp` and `src/app_dialogs.cpp` is now
+  mostly a thin dialog dispatch surface.
 - `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
@@ -171,6 +174,9 @@ Current architecture mismatches that must be treated as real blockers:
   in `src/platform_windows/windows_stylus_input.cpp` instead of `src/main.cpp`,
   while the retained Win32 VR/HMD shell now also routes through
   `src/platform_windows/windows_vr_shell.h` instead of staying inline in
+  `src/main.cpp`, while RenderDoc startup/frame capture, SHCore DPI bootstrap,
+  Win32 error-string conversion, and the GL debug pre/post callbacks now also
+  live in `src/platform_windows/windows_bootstrap_helpers.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