refactor(host/W6.2): extract the Linux zero-copy GPU plumbing into the pf-zerocopy leaf crate

linux/zerocopy/* (CUDA context/buffers + EGL/Vulkan dmabuf import + the isolated
import worker) and linux/dmabuf_fence.rs move wholesale into crates/pf-zerocopy,
so the coming pf-frame vocabulary crate (FramePayload::Cuda owns a DeviceBuffer)
and the pf-encode/pf-capture subsystem crates can reach the GPU plumbing without
the host orchestrator in between (plan §W6). Content stays Linux-only; the crate
compiles to an empty lib elsewhere, so dependents carry a plain dependency.

drm_fourcc deliberately does NOT move: it consumes the frame vocabulary
(PixelFormat), which sits ABOVE pf-zerocopy — it lives with capture for now and
moves into pf-frame next. cuda's ffi re-export bumps pub(crate)->pub (the raw
CUdeviceptr vocabulary is consumed across the crate boundary by the encode
backends). A crate::zerocopy shim module keeps every existing path valid until
capture/encode themselves move out.

Verified: Linux clippy -D warnings (pf-zerocopy --all-targets + host
nvenc,vulkan-encode,pyrowave --all-targets) + 17/17 pf-zerocopy tests + 321/321
host tests; Windows clippy nvenc,amf-qsv --all-targets Finished exit 0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/pf-zerocopy/Cargo.toml

@@ -0,0 +1,32 @@
+# The Linux GPU zero-copy plumbing (plan §9 / §W6), extracted into a leaf crate so the shared
+# frame vocabulary (pf-frame `FramePayload::Cuda`), the encode backends (CUDA copies/context),
+# and the capture import machinery can all reach it WITHOUT the host orchestrator in between.
+# Content is Linux-only; the crate compiles to an empty lib elsewhere so dependents can carry a
+# plain (non-target-gated) dependency.
+[package]
+name = "pf-zerocopy"
+version = "0.12.0"
+edition = "2021"
+# Inherit the workspace MSRV: clippy keys MSRV-gated lints off it (without this, e.g.
+# `manual_is_multiple_of` fires on code the host crate compiles clean).
+rust-version.workspace = true
+license = "MIT OR Apache-2.0"
+description = "punktfunk host Linux zero-copy GPU plumbing: CUDA context/buffers, EGL/Vulkan dmabuf import, the isolated import worker, and dmabuf implicit-fence sync."
+publish = false
+
+[target.'cfg(target_os = "linux")'.dependencies]
+anyhow = "1"
+tracing = "0.1"
+libc = "0.2"
+# `libcuda.so.1` is dlopen'd at runtime (NOT link-time) so one Linux binary runs on NVIDIA
+# (zero-copy via CUDA) AND on AMD/Intel (VAAPI, no NVIDIA driver present) — see `cuda::ffi`.
+libloading = "0.8"
+# EGL imports the PipeWire dmabuf, CUDA maps it (`dynamic` = load the NVIDIA libEGL at runtime).
+khronos-egl = { version = "6", features = ["dynamic"] }
+# Vulkan bridge for LINEAR dmabufs (gamescope): VK_EXT_external_memory_dma_buf import,
+# GPU-copy into an exportable allocation, export OPAQUE_FD → cuImportExternalMemory.
+ash = "0.38"
+# The isolated import worker's control protocol: small serde_json blobs over a Unix socket
+# (SCM_RIGHTS carries the fds; pixels never cross the socket).
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"