feat(encode): native QSV backend — libvpl-sys + qsv.rs (Phases 0-3 of design/native-qsv-encoder.md)

Vendored MIT VPL dispatcher (static, trimmed tree, pin 674d015b/v2.17.0) built
via cmake+bindgen behind new feature 'qsv' (pf-encode + punktfunk-host forward).
qsv.rs: dispatcher session on the capture adapter (LUID-matched), SetHandle
D3D11, AsyncDepth=1/GopRefDist=1/VDEnc/CBR + HRD-off low-latency config,
GetSurfaceForEncode + GPU CopySubresourceRegion input (zero-copy, no readback
path), bounded sync-point poll, in-place reset with teardown escalation, no-IDR
bitrate retarget (Reset + StartNewSequence=OFF), 10-bit P010 HEVC-Main10/AV1,
HDR mastering/CLL SEI-OBU at IDR + BT.2020/PQ VSI, LTR-RFI via mfxExtRefListCtrl
(AMF slot policy port, Query-gated per codec, wire-index FrameOrder pinning).
Dispatch: native-first with ffmpeg fallback + PUNKTFUNK_QSV_FFMPEG hatch;
probes (can_encode_10bit / windows_codec_support / windows_backend_is_probed)
now answer natively for QSV.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/libvpl-sys/vendor/libvpl/api/vpl/mfx.h

@@ -0,0 +1,31 @@
+/*############################################################################
+  # Copyright Intel Corporation
+  #
+  # SPDX-License-Identifier: MIT
+  ############################################################################*/
+
+#ifndef __MFX_H__
+#define __MFX_H__
+
+#include "mfxdefs.h"
+#include "mfxcommon.h"
+#include "mfxstructures.h"
+#include "mfxdispatcher.h"
+#include "mfximplcaps.h"
+#include "mfxsession.h"
+#include "mfxvideo.h"
+#include "mfxadapter.h"
+
+#include "mfxbrc.h"
+#include "mfxmvc.h"
+#include "mfxpcp.h"
+#include "mfxvp8.h"
+#include "mfxjpeg.h"
+
+#include "mfxsurfacepool.h"
+
+#ifdef ONEVPL_EXPERIMENTAL
+#include "mfxencodestats.h"
+#endif
+
+#endif /* __MFXDEFS_H__ */