Add capture pipeline rate + latency metrics to the Video panel

The FPS readout only measured the host's own render rate, hiding capture stutter.
The Video panel now shows a "Pipeline rates" section:
- Tool render (host FPS / frametime, as before);
- hooked source: Game present (/s, from VideoShare.present_calls deltas), Hook
  publish (/s, generation deltas), and capture->display latency avg/min/max ms;
- WGC source: WGC capture (/s) from a new WindowCapture frame-arrival counter
  (game present + latency are n/a, since WGC frames aren't game-timestamped).

Latency uses a system-wide clock: protocol v11->v12 adds VideoShare.present_qpc,
stamped by the hook at publish (publish_video_frame); the host measures
now_qpc - present_qpc per newly published frame, windowed to min/avg/max each second.

Verified: present_hook_test (x64 + x86) now asserts present_qpc is stamped; full
build x64 + x86 clean; ctest x64 9/9, x86 3/3. The live rate/latency numbers need a
real game mirroring to read meaningfully; wiring validated.

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

host/src/capture/window_capture.hpp

@@ -46,6 +46,12 @@ public:
 		return height_;
 	}
 
+	// Cumulative frames WGC has delivered (for the capture-rate metric).
+	[[nodiscard]] std::uint64_t frames_arrived() const
+	{
+		return frames_arrived_;
+	}
+
 	// Render thread: consume the newest frame (if any) and draw it letterboxed
 	// into a dst_w x dst_h target via `renderer`.
 	void draw_latest(FrameRenderer& renderer, ID3D11DeviceContext* ctx, std::uint32_t dst_w, std::uint32_t dst_h);
@@ -60,6 +66,7 @@ private:
 	Microsoft::WRL::ComPtr<ID3D11ShaderResourceView> latest_srv_;
 	std::uint32_t width_ = 0;
 	std::uint32_t height_ = 0;
+	std::uint64_t frames_arrived_ = 0; // incremented in on_frame_arrived
 
 	std::mutex mutex_; // guards pending_ handoff only (no context work under it)
 	winrt::Windows::Graphics::Capture::Direct3D11CaptureFrame pending_{nullptr};