Route app shutdown staging through app core

docs/modernization/roadmap.md

@@ -203,6 +203,11 @@ gating, canvas-stroke drawing, VR UI drawing, main UI drawing, and redraw reset
 now live in `pp_app_core`; `App::create`, `App::update`, `App::draw`, and
 `pano_cli plan-app-frame` consume those plans while retained layout traversal
 and OpenGL/UI drawing stay in the legacy app.
+Shutdown lifecycle staging for UI-state save, stroke-preview renderer shutdown,
+recording stop, texture/shader invalidation, layout unload, render-target
+destruction, panel-node release, and quick-mode cleanup now lives in
+`pp_app_core`; `App::terminate` and `pano_cli plan-app-shutdown` consume that
+plan while retained cleanup execution stays in the legacy app.
 `panopainter_app` is now a real static target that owns app orchestration
 sources, app version metadata, and version-header generation.
 `pp_panopainter_ui` now owns app-specific modal, dialog, panel, canvas,
@@ -1291,7 +1296,7 @@ standard x64/arm64, Android Quest arm64, Android Focus/Wave arm64,
 Emscripten/WebGL, macOS, iOS device, and iOS simulator. `platform-build`
 automation now builds the current headless component matrix, including
 `pp_platform_api`, `pp_app_core`, platform API tests, brush-package tests, and
-the current app-core startup/frame/file/document/brush/canvas/history/grid/toolbar/
+the current app-core startup/frame/shutdown/file/document/brush/canvas/history/grid/toolbar/
 tools/about/preferences/status automation tests. The PowerShell wrapper also
 normalizes comma-separated `-Presets` and `-Targets` values for reliable
 machine-driven partial matrix checks. `panopainter_platform_build_target_matrix_self_test`
@@ -1653,6 +1658,11 @@ Results:
 - Focused frame CTest coverage passed for `pp_app_core_app_frame_tests`,
   `pano_cli_plan_app_frame_vr_smoke`, and
   `pano_cli_plan_app_frame_idle_missing_canvas_smoke`.
+- `PanoPainter`, `pp_app_core_app_shutdown_tests`, and `pano_cli` built after
+  shutdown cleanup staging moved into `pp_app_core`.
+- Focused shutdown CTest coverage passed for `pp_app_core_app_shutdown_tests`,
+  `pano_cli_plan_app_shutdown_smoke`, and
+  `pano_cli_plan_app_shutdown_rejects_unknown_option`.
 - `PanoPainter`, `pp_app_core_brush_package_export_tests`, and `pano_cli` built
   after PPBR brush package export request validation and dispatch moved behind
   app-core brush package services.