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/punktfunk-host/Cargo.toml

@@ -280,6 +280,12 @@ nvenc = ["pf-encode/nvenc"]
 # (BtbN lgpl-shared with `*_amf`/`*_qsv`) at build and bundles the FFmpeg DLLs at runtime. Build the
 # all-vendor GPU host with `--features nvenc,amf-qsv`.
 amf-qsv = ["pf-encode/amf-qsv"]
+# Native Intel QSV via the statically linked VPL dispatcher (Windows). OFF by default: needs
+# cmake + libclang at build (both already required by pyrowave); runtime GPU libs come from the
+# Intel driver store, so the same binary starts fine on NVIDIA/AMD boxes. Supersedes the ffmpeg
+# QSV path (design/native-qsv-encoder.md). ⚠ Like `nvenc`: hand builds for Intel boxes need
+# `--features qsv` or QSV falls back to ffmpeg (if `amf-qsv`) / software.
+qsv = ["pf-encode/qsv"]
 # Raw Vulkan Video HEVC/AV1 encode on Linux (AMD/Intel) — real reference-frame-invalidation loss
 # recovery via explicit DPB reference slots (design/linux-vulkan-video-encode.md). OFF by default;
 # reuses pf-encode's `ash` bindings (no new dep). Runtime-gated further by PUNKTFUNK_VULKAN_ENCODE.