perf(host/windows): move capture→encode off the 3D engine (NV12/P010 video-processor path, zero-copy, GPU priority)

The Windows host capped at ~60 fps with 35-40 ms latency on a GPU-heavy game:
the per-frame capture→encode path shared the 3D engine with the game and got
scheduled behind it. Rework to minimize 3D-engine work per frame:

- VideoConverter (D3D11 video processor): capture → NVENC-native NV12/P010 so
  NVENC skips its internal RGB→YUV (a 3D/compute step). Wired into both DDA
  (dxgi.rs) and WGC (wgc.rs). New PixelFormat::Nv12/P010 + NVENC YUV input.
- GPU scheduling hardening (Apollo-style): D3DKMTSetProcessSchedulingPriorityClass
  HIGH, absolute SetGPUThreadPriority, SetMaximumFrameLatency(1).
- WGC SDR zero-copy (hold pool frames; no CopyResource). DDA keeps a fast
  CopyResource to decouple its single-frame acquire/release from the async convert.
- Pipelined helper encode loop (PUNKTFUNK_ENCODE_DEPTH, default 1) + perf split
  (cap_wait / encode / write).

Live on the RTX 4090: hard 60 fps ceiling removed (now scene-scaling 40-200+),
latency much reduced. Residual cap in GPU-pinned scenes is the irreducible RGB→YUV
convert (no fixed-function unit on NVIDIA — VideoProcessing engine reads 0%) waiting
behind an uncapped game under WDDM context time-slicing; Linux avoids it via
gamescope capping the game to the display refresh.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/punktfunk-host/src/zerocopy/mod.rs

@@ -36,8 +36,8 @@ pub fn drm_fourcc(format: crate::capture::PixelFormat) -> Option<u32> {
         Rgbx => fourcc(b"XB24"), // DRM_FORMAT_XBGR8888
         Rgba => fourcc(b"AB24"), // DRM_FORMAT_ABGR8888
         // 24-bit packed RGB/BGR have no straightforward dmabuf import here; use the CPU path.
-        // Rgb10a2 is the Windows HDR capture format — never produced by the Linux capturer.
-        Rgb | Bgr | Rgb10a2 => return None,
+        // Rgb10a2/Nv12/P010 are the Windows HDR / video-processor formats — never produced on Linux.
+        Rgb | Bgr | Rgb10a2 | Nv12 | P010 => return None,
     })
 }