Own legacy platform services on Linux

docs/modernization/roadmap.md

@@ -70,6 +70,12 @@ What is already real:
 - `pp_app_core`
 
 Latest slice:
+- `src/platform_legacy/legacy_platform_services.*` now exposes an ownable
+  `create_platform_services()` entrypoint alongside the legacy fallback
+  accessor.
+- `linux/src/main.cpp` now owns a local legacy `PlatformServices` instance and
+  binds it into `App` explicitly instead of binding the process-global legacy
+  accessor directly.
 - `src/app_events.cpp` no longer silently falls back to
   `pp::platform::legacy::platform_services()` when `App` has no bound platform
   services; the live app path now expects explicit platform-service ownership.

docs/modernization/tasks.md

@@ -78,6 +78,12 @@ Completed, blocked, and superseded task history moved to
   the queue is now ordered by code movement instead.
 
 Current slice:
+- `src/platform_legacy/legacy_platform_services.*` now exposes an ownable
+  `create_platform_services()` entrypoint while keeping the fallback singleton
+  for non-migrated platforms.
+- `linux/src/main.cpp` now binds an owned legacy `PlatformServices` instance
+  into `App`, making Linux the first explicit per-entrypoint owner of that
+  legacy service implementation.
 - `src/app_events.cpp` no longer hides a fallback to
   `pp::platform::legacy::platform_services()`; touched app platform dispatch
   now expects an explicitly bound platform-services pointer.