Route export storage hooks through platform services

docs/modernization/roadmap.md

@@ -1,7 +1,7 @@
 # PanoPainter Modernization Roadmap
 
 Status: live
-Last updated: 2026-06-03
+Last updated: 2026-06-04
 
 This is the living roadmap for modernizing PanoPainter into independently
 testable C++23 components while retaining all existing functionality. Keep this
@@ -639,6 +639,10 @@ is preserved while their platform shell implementations are extracted.
 Prepared-file save/download handoff is now also part of the service contract,
 so iOS/Web export completion routes through `PlatformServices` after the app
 writes the temporary/exported payload.
+Canvas image export publishing and explicit persistent-storage flushes now
+dispatch through `PlatformServices` too, preserving iOS photo-library export
+publication and WebGL filesystem sync behavior in the legacy adapter while
+removing those direct platform calls from `Canvas` and brush preset storage.
 `App::show_cursor`, `App::hide_cursor`, `App::showKeyboard`, and
 `App::hideKeyboard` now dispatch through the active service without local
 platform guards; unsupported platforms rely on their service no-op behavior.
@@ -1679,7 +1683,8 @@ Results:
   app/window close dispatch, UI-thread lifecycle dispatch, render-context
   lifecycle dispatch, render-target binding dispatch, render platform hint
   dispatch, render debug callback dispatch, render-capture frame hook dispatch,
-  recording cleanup dispatch, live asset/layout reload policy dispatch,
+  recording cleanup dispatch, exported-image publish dispatch, persistent
+  storage flush dispatch, live asset/layout reload policy dispatch,
   diagnostic hook dispatch, per-frame platform hook dispatch, picker callback
   dispatch, and prepared-file save/download callback dispatch. The live Windows
   app now