feat(clients/windows): D3D11VA hardware decode in the session client — Vulkan chain becomes vulkan → d3d11va → software

The vendor-agnostic DXVA path for GPUs without Vulkan Video (Intel's Windows driver foremost,
which previously landed on CPU decode). Ported from the retired WinUI presenter's decoder with
its Intel-safe discipline intact (decode pool stays libavcodec-derived — a hand-built pool
broke Intel at the first SubmitDecoderBuffers), on a decode device LUID-matched to the
presenter's adapter.

Hand-off is a ring of shareable BGRA8 textures (SHARED_NTHANDLE | SHARED_KEYEDMUTEX) filled by
the fixed-function ID3D11VideoProcessor (NV12/P010 → BGRA8, colour spaces from the per-frame
CICP; PQ is tone-mapped to SDR by the processor — HDR-first boxes take Vulkan Video). BGRA is
deliberate: importing a multiplanar NV12 D3D11 texture device-losts on NVIDIA however it is
consumed (plane-view sampling and DMA copy both validation-clean, both TDR — bisected), while
single-plane RGBA D3D11↔Vulkan interop is the path Chromium/ANGLE exercise on every driver.
The presenter imports a slot's NT handle per frame (VK_KHR_external_memory_win32, gated on the
spec-required external-format probe) and blits it into the video image — no CSC pass; the DXGI
keyed mutex (key 0 both sides, drop-tolerant) is the cross-API lock and visibility barrier.

Verified live vs a real host at 5120x1440@240 HEVC on an RTX 4090: 240 fps, e2e 2.7/3.0 ms
p50/p95 under the Khronos validation layer — parity with Vulkan Video (2.6 ms); auto still
resolves vulkan on NVIDIA. PUNKTFUNK_DECODER=d3d11va forces it; import/present failures demote
to software on the existing streak contract.

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

crates/pf-presenter/src/lib.rs

@@ -10,11 +10,14 @@
 //! import/present failure streak, demote the decoder to software via the session pump's
 //! `force_software` contract, same as the GTK presenter.
 //!
-//! Builds on Linux AND Windows; `dmabuf` is the one Linux-only module (DRM-PRIME does
-//! not exist on Windows — the decode chain there is Vulkan → software).
+//! Builds on Linux AND Windows; `dmabuf` is Linux-only (DRM-PRIME does not exist on
+//! Windows) and `d3d11` is its Windows counterpart (D3D11VA shared-texture import) —
+//! the decode chain there is Vulkan → D3D11VA → software.
 
 #[cfg(any(target_os = "linux", windows))]
 pub mod csc;
+#[cfg(windows)]
+pub mod d3d11;
 #[cfg(target_os = "linux")]
 pub mod dmabuf;
 #[cfg(any(target_os = "linux", windows))]