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/PUNKTFUNK-VENDOR.txt

@@ -0,0 +1,14 @@
+Upstream: https://github.com/intel/libvpl
+Pin:      674d015bcb294bc39fa276e99a652ea045423e82 (v2.17.0 per version.txt, 2026-07)
+License:  MIT (LICENSE; third-party notices in third-party-programs.txt)
+
+Trimmed vendor tree: only what the static dispatcher build + bindgen need.
+Dropped from upstream: examples/, doc/, env/, script/, tools, api/strings/,
+api/tests/, libvpl/test/, top-level CMakeLists.txt (replaced by the crate-root
+CMakeLists.txt one level up, which pins BUILD_SHARED_LIBS=OFF, all INSTALL_*
+off, BUILD_EXPERIMENTAL=ON).
+
+BUILD_EXPERIMENTAL=ON defines ONEVPL_EXPERIMENTAL: the D3D11 surface-import
+API (mfxMemoryInterface / mfxSurfaceD3D11Tex2D) is experimental ABI that is
+release-coupled — bumping this pin requires re-checking every ONEVPL_EXPERIMENTAL
+symbol qsv.rs touches (design/native-qsv-encoder.md §3.1/§3.4).