feat(client/windows): HDR10 (BT.2020 PQ) decode + present

Light up the dormant 10-bit/HDR path end to end on the Windows client.

- core: NativeClient::connect gains a video_caps param threaded into the Hello. The Windows
  client advertises VIDEO_CAP_10BIT | VIDEO_CAP_HDR; every other caller (the C ABI shim,
  Linux, Android, host test connects) passes 0, so the 8-bit BT.709 path is unchanged. The
  host already gates a Main10/PQ encode on these bits + PUNKTFUNK_10BIT.
- video.rs: a PQ frame (color_trc == SMPTE2084) converts 10-bit YUV → X2BGR10 (== DXGI
  R10G10B10A2) with the BT.2020 matrix via sws_setColorspaceDetails; swscale applies only
  the matrix + range, so the PQ-encoded samples pass through untouched.
- present.rs: on an HDR frame the swapchain flips in place (ResizeBuffers) to R10G10B10A2 +
  DXGI_COLOR_SPACE_RGB_FULL_G2084_NONE_P2020 + HDR10 metadata; the passthrough shader is
  unchanged and the compositor maps PQ→display. Switched to ALPHA_MODE_IGNORE so the 10-bit
  padding bits don't render transparent. SDR stays 8-bit B8G8R8A8.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/m3.rs

@@ -3180,6 +3180,7 @@ mod tests {
                 CompositorPref::Auto,
                 GamepadPref::Auto,
                 0,
+                0, // video_caps
                 None, // launch
                 None,
                 Some((cert.clone(), key.clone())),
@@ -3211,6 +3212,7 @@ mod tests {
             CompositorPref::Auto,
             GamepadPref::Auto,
             0,
+            0, // video_caps
             None, // launch
             None,
             Some((cert, key)),
@@ -3271,6 +3273,7 @@ mod tests {
                 CompositorPref::Auto,
                 GamepadPref::Auto,
                 0,
+                0, // video_caps
                 None, // launch
                 None,
                 None,
@@ -3297,6 +3300,7 @@ mod tests {
             CompositorPref::Auto,
             GamepadPref::Auto,
             0,
+            0, // video_caps
             None, // launch
             Some(host_fp),
             Some((cert.clone(), key.clone())),