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-client-core/Cargo.toml

@@ -44,3 +44,16 @@ sdl3 = { version = "0.18", features = ["hidapi"] }
 [target.'cfg(windows)'.dependencies]
 wasapi = "0.23"
 sdl3 = { version = "0.18", features = ["hidapi", "build-from-source"] }
+# D3D11VA decode (video_d3d11.rs): device/adapter selection, DXVA probes, and the shared
+# NT-handle hand-off ring. Same pinned rev as clients/windows so the workspace builds ONE
+# windows-rs.
+windows = { git = "https://github.com/microsoft/windows-rs", rev = "a4f7b2cb7c63c6bb7fc77a2affe57145be1d8c4f", features = [
+    "Win32_Foundation",
+    "Win32_Graphics_Direct3D",
+    "Win32_Graphics_Direct3D11",
+    "Win32_Graphics_Dxgi",
+    "Win32_Graphics_Dxgi_Common",
+    # IDXGIResource1::CreateSharedHandle takes an optional SECURITY_ATTRIBUTES — the
+    # method itself is feature-gated behind this.
+    "Win32_Security",
+] }