refactor(host/W6.2): extract virtual-display orchestration into the pf-vdisplay crate

vdisplay.rs + vdisplay/* (the per-compositor Linux backends — KWin zkde-screencast,
wlroots swaymsg, Mutter RemoteDesktop, Hyprland — and the Windows IddCx/pf-vdisplay
driver backend, behind one VirtualDisplay trait; the mode-conflict admission
registry, the display policy/identity/custom-preset state, and the session-env /
gamescope routing) move into crates/pf-vdisplay (plan §W6). The DDC/CI panel-power
control (used only here) and the KWin zkde protocol XML move with it. This
completes the host-crate decomposition: capture, encode, inject, and vdisplay are
now four subsystem crates over the shared leaves, and punktfunk-host is the
orchestrator (serve/supervisor + native + gamestream + mgmt).

Coupling breaks (all down-only, cargo-tree acyclic):
- capture::dxgi identity -> pf_frame::dxgi; win_display/monitor_devnode/
  console_session_mismatch -> pf-win-display leaf; can_open_another_session ->
  pf-encode (the NVENC session-budget admission gate — acyclic peer edge).
- The registry's DisplayCreated/DisplayReleased emits into the host SSE event bus
  invert to a leaf hook: pf-vdisplay emits a neutral DisplayEvent to a
  host-registered DISPLAY_EVENT_SINK, so it never reaches the orchestrator's
  events module.
- The IddCx driver module is renamed pf_vdisplay -> driver (its old name collided
  with the crate name through the host's `mod vdisplay` shim glob).

The host keeps `mod vdisplay { pub use pf_vdisplay::* }` so every crate::vdisplay::*
path (serve/mgmt/native/the capture FrameChannelSender seam) is unchanged; the
heavy deps (wayland/ashpd/tokio + the zkde protocol) moved with the crate.
Co-authored: a fail-closed IOCTL-reply-length security fix (reject short/zeroed
pf-vdisplay driver replies before trusting protocol_version/target_id/wudf_pid/luid,
security-review 2026-07-17) rides this commit in the moved driver module.

Verified: Linux clippy -D warnings (pf-vdisplay + host nvenc,vulkan-encode,pyrowave
--all-targets) + pf-vdisplay 63/63 + host 167/167 tests; Windows clippy -D warnings
(pf-vdisplay --all-targets + host nvenc,amf-qsv --all-targets) Finished exit 0.

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

crates/punktfunk-host/Cargo.toml

@@ -38,6 +38,9 @@ pf-capture = { path = "../pf-capture" }
 # subsystem crate (plan §W6). Consumes core::input; the heavy input deps (wayland/reis/xkbcommon/
 # usbip) moved with it.
 pf-inject = { path = "../pf-inject" }
+# Virtual-display orchestration (per-compositor Linux backends + the Windows IddCx driver backend),
+# extracted to a subsystem crate (plan §W6). The DDC panel control + KWin zkde protocol moved with it.
+pf-vdisplay = { path = "../pf-vdisplay" }
 # M3 native control plane (the `punktfunk/1` QUIC handshake; data plane stays native-thread UDP).
 quinn = "0.11"
 anyhow = "1"