Split Apple platform target and move platform state ownership

docs/modernization/roadmap.md

@@ -92,6 +92,20 @@ Current hotspot files:
 
 Latest slice:
 
+- `pp_platform_api` no longer compiles
+  `src/platform_apple/apple_platform_services.*`; Apple concrete platform
+  code now lives in the new `pp_platform_apple` target, and
+  `panopainter_app` plus `pp_platform_api_tests` link that concrete target
+  where needed.
+- Retained GLFW window hooks/state and retained Apple UI/app handle snapshots
+  now live in `src/platform_legacy/legacy_platform_state.*` instead of staying
+  inline in `src/platform_legacy/legacy_platform_services.cpp`, which trims
+  another process-global platform-state pocket out of the legacy platform
+  shell and removes more direct `App::I` reads from touched platform paths.
+- Windows VR session snapshot ownership now lives in
+  `src/platform_windows/windows_vr_shell.h` and
+  `src/platform_windows/windows_platform_services.*` instead of on `App`,
+  with app-side reads now routed through `App::vr_session_snapshot()`.
 - The live Windows entry shell now routes through
   `run_main_application(...)` in
   `src/platform_windows/windows_runtime_shell.*`, leaving `src/main.cpp` as a
@@ -172,8 +186,9 @@ Latest slice:
 
 Current architecture mismatches that must be treated as real blockers:
 
-- `pp_platform_api` still compiles Apple implementation files instead of only
-  platform-neutral policy and interface code.
+- `pp_platform_api` no longer compiles Apple implementation files, but it
+  still owns concrete Linux platform sources instead of only platform-neutral
+  policy and interface code.
 - `src/platform_apple/apple_platform_services.cpp` no longer reaches `App::I`
   directly, and Linux FPS title reporting now uses an injected callback, but
   retained Apple bridging in `platform_legacy` and other platform/app coupling
@@ -185,8 +200,10 @@ Current architecture mismatches that must be treated as real blockers:
   route through retained local GLFW callback hooks, and retained Apple ObjC
   handles plus storage paths now sit behind one local `platform_legacy`
   helper instead of being re-read through `App::I` in each touched path, with
-  the retained GLFW window hooks and fallback storage-path return now also
-  using local retained-state helpers instead of direct method-body reads.
+  the retained GLFW window hooks, Apple handle snapshots, and fallback
+  storage-path return now also using local retained-state helpers instead of
+  direct method-body reads, while Windows VR session snapshot state now also
+  lives behind platform-owned helpers instead of on `App`.
 - `src/platform_legacy/legacy_platform_services.*` is still part of the live
   app shell.
 - `pp_panopainter_ui` still depends on `pp_legacy_app`.