refactor(host/W6.2): extract the frame-capture backends into the pf-capture crate

capture/linux (PipeWire portal) + capture/windows (IDD direct-push: dxgi
mechanics, idd_push + submodules, synthetic_nv12) + pwinit move into
crates/pf-capture behind the Capturer trait + synthetic sources (plan §W6).
The crate speaks pf-frame (CapturedFrame/PixelFormat + the DXGI identity),
pf-zerocopy (CUDA import), and the pf-win-display leaves, and NEVER pf-encode —
the capture->encode edge is one-way. This completes the deliberate capture/encode
crate split (the invasive path the plan had merged into one pf-media): capture
and encode are now separate subsystem crates sharing only pf-frame.

Four seams keep the capturer off the orchestrator:
- VirtualOutput is EXPLODED into primitives (remote_fd/node_id/preferred_mode/
  keepalive) by the host facade, so pf-capture never depends on the vdisplay type;
- FrameChannelSender: the sealed-channel delivery is a Send+Sync closure the host
  facade builds from the pf-vdisplay control device + send_frame_channel IOCTL and
  hands in; ChannelBroker holds the closure instead of the control HANDLE (the
  whole-desktop handle-duplication security boundary is byte-for-byte unchanged);
- console_session_mismatch + desktop_bounds live in pf-win-display (leaf peers);
- pwinit moves here (audio caller -> pf_capture::pwinit).

The host keeps capture.rs as a thin BRIDGE: it re-exports the vocabulary + capturer
types (every crate::capture::* path is unchanged) and keeps open_portal_monitor /
capture_virtual_output, which resolve the ZeroCopyPolicy + FrameChannelSender and
call into pf-capture. verify_is_wudfhost + install_gpu_pref_hook are re-exported
(the gamepad-channel bootstrap + the main.rs subcommand consume them).

Co-developed: the resident-HID-mouse compose-kick hook (HID_COMPOSE_KICK + the
HID-first cursor kick + _display_wake) rides this commit into pf-capture; the host
mouse_windows registration side lands separately on top.

Verified: Linux clippy -D warnings (pf-capture + host nvenc,vulkan-encode,pyrowave
--all-targets) + host tests 299/299; Windows clippy -D warnings (pf-capture
--all-targets + host nvenc,amf-qsv --all-targets) Finished exit 0.

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

crates/pf-capture/Cargo.toml

@@ -0,0 +1,52 @@
+# Frame capture (plan §7 / §W6): the Linux xdg-ScreenCast/PipeWire portal capturer and the Windows
+# IDD direct-push capturer, plus the synthetic sources + the Capturer trait, extracted into a
+# subsystem crate. Depends on the shared frame vocabulary (pf-frame), the zero-copy plumbing
+# (pf-zerocopy), and the display leaves (pf-win-display) — never on pf-encode: the encode-backend
+# facts arrive pre-resolved (ZeroCopyPolicy) and the sealed-channel delivery as a closure
+# (FrameChannelSender), so the capture→encode edge is one-way (plan §2.4).
+[package]
+name = "pf-capture"
+version = "0.12.0"
+edition = "2021"
+rust-version.workspace = true
+license = "MIT OR Apache-2.0"
+description = "punktfunk host frame capture: Linux PipeWire portal + Windows IDD direct-push capturers behind one Capturer trait."
+publish = false
+
+[dependencies]
+punktfunk-core = { path = "../punktfunk-core", features = ["quic"] }
+pf-frame = { path = "../pf-frame" }
+pf-zerocopy = { path = "../pf-zerocopy" }
+pf-win-display = { path = "../pf-win-display" }
+pf-gpu = { path = "../pf-gpu" }
+pf-host-config = { path = "../pf-host-config" }
+anyhow = "1"
+tracing = "0.1"
+
+[target.'cfg(target_os = "linux")'.dependencies]
+# The xdg ScreenCast + RemoteDesktop portals, and the PipeWire consumer for the capture frames.
+ashpd = { version = "0.13", features = ["screencast", "remote_desktop"] }
+pipewire = "0.9"
+libc = "0.2"
+# ashpd 0.13 uses the tokio runtime for the one-time portal handshake (control plane).
+tokio = { version = "1", features = ["rt", "rt-multi-thread", "net", "time"] }
+
+[target.'cfg(target_os = "windows")'.dependencies]
+# The host<->driver wire contract for the sealed frame channel (control IOCTL structs + frame header).
+pf-driver-proto = { path = "../pf-driver-proto" }
+windows = { version = "0.62", features = [
+    "Win32_Foundation",
+    "Win32_Security",
+    "Win32_Security_Authorization",
+    "Win32_Graphics_Direct3D",
+    "Win32_Graphics_Direct3D11",
+    "Win32_Graphics_Direct3D_Fxc",
+    "Win32_Graphics_Dxgi",
+    "Win32_Graphics_Dxgi_Common",
+    "Win32_System_LibraryLoader",
+    "Win32_System_Memory",
+    "Win32_System_Threading",
+    "Win32_UI_HiDpi",
+    "Win32_UI_Input_KeyboardAndMouse",
+    "Win32_UI_WindowsAndMessaging",
+] }