Read/write the cross-process diagnostic counters atomically

present_calls, frames_dropped (VideoShare) and frames_rendered (AudioStreamInfo)
were plain `+= 1` / stores in the DLL, read by the host cross-process. On an x86
DLL a 64-bit store is two halves, so the x64 host could read a torn value during
a carry. Benign (display-only), but a real data race.

Use std::atomic_ref at the access sites rather than changing the field types:
the structs stay plain POD so the layout/offset asserts are unchanged and
AudioStreamInfo stays trivially copyable (it's published/read as a whole struct).
The DLL writers (note_present / note_video_dropped / note_audio_frames) and the
host readers (IpcServer::video_share / hook_status) now use relaxed atomic_ref;
hook_status reloads frames_rendered atomically after the wholesale struct copy.
The dev-tool readers (vk_validate, audio_probe) keep plain reads -- diagnostics of
diagnostics, and same-bitness in practice.

Validated by present_hook_test (present_calls via atomic_ref) and audio_hook_test
(frames_rendered) -- also confirms no atomic_ref alignment fault.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

hook/src/ipc_client.hpp

@@ -200,7 +200,10 @@ public:
 	{
 		if (block_ != nullptr && slot < kMaxAudioStreams)
 		{
-			block_->status.audio_streams[slot].frames_rendered = frames;
+			// atomic_ref so the host's cross-process read isn't torn (notably an x86 DLL -> x64 host,
+			// where a plain 64-bit store is two halves). The field stays plain POD so AudioStreamInfo
+			// remains trivially copyable for the wholesale publishes elsewhere.
+			std::atomic_ref(block_->status.audio_streams[slot].frames_rendered).store(frames, std::memory_order_relaxed);
 		}
 	}
 
@@ -211,7 +214,7 @@ public:
 	{
 		if (block_ != nullptr)
 		{
-			block_->video.present_calls += 1;
+			std::atomic_ref(block_->video.present_calls).fetch_add(1, std::memory_order_relaxed);
 		}
 	}
 
@@ -221,7 +224,7 @@ public:
 	{
 		if (block_ != nullptr)
 		{
-			block_->video.frames_dropped += 1;
+			std::atomic_ref(block_->video.frames_dropped).fetch_add(1, std::memory_order_relaxed);
 		}
 	}