Extract app frame and export dialog helpers

docs/modernization/roadmap.md

@@ -86,9 +86,9 @@ Current hotspot files:
 - `src/main.cpp`: 1117 lines
 - `src/node_panel_brush.cpp`: 1197 lines
 - `src/node_stroke_preview.cpp`: 933 lines
-- `src/node_canvas.cpp`: 953 lines
-- `src/app.cpp`: 950 lines
-- `src/app_dialogs.cpp`: 789 lines
+- `src/node_canvas.cpp`: 897 lines
+- `src/app.cpp`: 502 lines
+- `src/app_dialogs.cpp`: 441 lines
 
 Current architecture mismatches that must be treated as real blockers:
 
@@ -139,7 +139,10 @@ Current architecture mismatches that must be treated as real blockers:
   `src/app_layout_about_layer_menu.cpp` and `App::init_menu_about()` plus
   `App::init_menu_layer()` are now thin call-throughs, while the informational
   overlay opener family now also lives in `src/app_dialogs_info_openers.cpp`
-  and the corresponding `App::dialog_*` entrypoints are thinner.
+  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.
 - `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
@@ -172,7 +175,12 @@ Current architecture mismatches that must be treated as real blockers:
   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
-  canvas state-management cluster for picking, clear/clear-all, layer
+  UI observer math, repeated UI child traversal, and canvas toolbar refresh
+  now live in `src/legacy_app_frame_services.cpp` instead of staying inline in
+  `src/app.cpp`, while the larger document/export/save/open/thumbnail
+  document-IO cluster now lives in `src/legacy_canvas_document_io_services.cpp`
+  and `src/app.cpp` is materially thinner,
+  while the canvas state-management cluster for picking, clear/clear-all, layer
   add/remove/order/lookups, animation frame control, resize, and snapshot
   save/restore now lives in `src/legacy_canvas_state_services.cpp` instead of
   `src/canvas.cpp`, while the larger import/export/save/open/thumbnail