feat(windows-host): STEP 4 (3/n) — host pf_vdisplay backend (talks to the new driver)

The host can now drive the new pf-vdisplay IddCx driver instead of SudoVDA. Compiles
clean on BOTH Windows (cargo check -p punktfunk-host green) and Linux (cfg(windows)-gated,
main CI unaffected); adversarially reviewed (no blockers, lockstep with the driver).

- new vdisplay/pf_vdisplay.rs: cloned from the proven sudovda.rs, repointed to
  pf_vdisplay_proto — interface GUID 70667664 (not e5bcc234), IOCTL 0x900-0x905 (not the
  gappy 0x800/0x888/0x8FF), AddRequest/AddReply/RemoveRequest/SetRenderAdapterRequest
  (bytemuck Pod, not the GUID-keyed AddParams), a u64 session_id monitor key (not a minted
  GUID), and a single IOCTL_GET_INFO handshake that HARD-asserts protocol_version (vs
  SudoVDA two-IOCTL best-effort). Full MGR/linger/refcount/teardown lifecycle preserved.
- reuses sudovda.rs backend-neutral CCD/DXGI helpers (set_active_mode, isolate/restore_
  displays_ccd, resolve_gdi_name, resolve_render_adapter_luid, MON_GEN/CURRENT_MON_GEN,
  SavedConfig) — widened to pub(crate), not duplicated.
- vdisplay::open()/probe() select the backend: PUNKTFUNK_VDISPLAY=pf|sudovda forces one;
  default auto-detects (prefer pf-vdisplay if its interface enumerates, else SudoVDA stays
  the shipping fallback).

Notes: SET_RENDER_ADAPTER is tolerated as the driver returns NOT_IMPLEMENTED today (STEP 4
tail); the cross-MGR wait_for_monitor_released only paces sudovda's MGR (benign until
IDD-push lands on pf-vdisplay, STEP 6 — documented in-code). On-glass "monitor appears at
WxH@Hz" gate is next.

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

crates/punktfunk-host/Cargo.toml

@@ -188,6 +188,12 @@ nvidia-video-codec-sdk = { version = "0.4", features = ["ci-check"], optional =
 # same BtbN gpl-shared tree the Windows client uses) and pulls the shared `avcodec/avutil/...` DLLs
 # at runtime. `ffmpeg-sys-next` auto-detects the FFmpeg version (7.x/avcodec-61 or 8.x/62).
 ffmpeg-next = { version = "8", optional = true }
+# Shared host<->driver wire contract for the pf-vdisplay IddCx virtual-display backend
+# (vdisplay/pf_vdisplay.rs): the control-plane IOCTL codes + `#[repr(C)] Pod` request/reply structs,
+# defined ONCE so host<->driver ABI drift is a compile error. `bytemuck` serializes those structs
+# to/from the DeviceIoControl byte buffers.
+pf-vdisplay-proto = { path = "../pf-vdisplay-proto" }
+bytemuck = { version = "1.19", features = ["derive"] }
 
 [features]
 # NVENC hardware encode (Windows). OFF by default: it pulls the NVENC SDK, and the host then needs