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>

Cargo.toml

@@ -22,6 +22,7 @@ members = [
     "crates/pf-inject",
     "crates/pf-vdisplay",
     "crates/pyrowave-sys",
+    "crates/libvpl-sys",
     "clients/probe",
     "clients/linux",
     "clients/session",