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/mfxpcp.h

@@ -0,0 +1,45 @@
+/*############################################################################
+  # Copyright Intel Corporation
+  #
+  # SPDX-License-Identifier: MIT
+  ############################################################################*/
+
+#ifndef __MFXPCP_H__
+#define __MFXPCP_H__
+#include "mfxstructures.h"
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif /* __cplusplus */
+
+/*! The Protected enumerator describes the protection schemes. */
+enum {
+    MFX_PROTECTION_CENC_WV_CLASSIC      = 0x0004, /*!< The protection scheme is based on the Widevine* DRM from Google*. */
+    MFX_PROTECTION_CENC_WV_GOOGLE_DASH  = 0x0005, /*!< The protection scheme is based on the Widevine* Modular DRM* from Google*. */
+};
+
+/* Extended Buffer Ids */
+enum {
+    MFX_EXTBUFF_CENC_PARAM          = MFX_MAKEFOURCC('C','E','N','P') /*!< This structure is used to pass decryption status report index for Common
+                                                                           Encryption usage model. See the mfxExtCencParam structure for more details. */
+};
+
+MFX_PACK_BEGIN_USUAL_STRUCT()
+/*!
+   Used to pass the decryption status report index for the Common Encryption usage model. The application can
+   attach this extended buffer to the mfxBitstream structure at runtime.
+*/
+typedef struct _mfxExtCencParam{
+    mfxExtBuffer Header;      /*!< Extension buffer header. Header.BufferId must be equal to MFX_EXTBUFF_CENC_PARAM. */
+
+    mfxU32 StatusReportIndex; /*!< Decryption status report index. */
+    mfxU32 reserved[15];
+} mfxExtCencParam;
+MFX_PACK_END()
+
+#ifdef __cplusplus
+} // extern "C"
+#endif /* __cplusplus */
+
+#endif