fix(agc): a replaced device's unit shadows leave the registry

When the windowless device is replaced at the first present, its unit
shadows were published but stayed registered. Lookups take the shadow
whose import starts nearest below an address, so such a stale entry
could hide the live import's shadow. The write-back results it held then
looked absent, and an upload read the import's stale bytes instead.
The replaced device's shadows are now dropped once it is idle.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

core/libs/prx/libSceAgcDriver/Execution/src/VulkanDevice.cpp

@@ -989,6 +989,7 @@ void VulkanDevice::PrepareForReplacement() {
     Graphics::FlushCachedTextures(state->device);
     Graphics::PublishAllShadows(state->context, Graphics::PublishReason::Teardown);
     WaitIdle();
+    Graphics::DestroyShadows(state->device);
 }
 
 void VulkanDevice::WaitIdle() {