feat(windows-drivers): pf-vdisplay STEP 0 scaffold + std-under-UMDF link gate

M1 step 2 begins. Add the wdk-iddcx (lib, re-exports wdk_sys::iddcx) + pf-vdisplay
(cdylib) workspace members. pf-vdisplay STEP 0 = DriverEntry + WdfDeviceCreate
skeleton + a #[used] _std_link_gate forcing std::thread + OwnedHandle to link, so
the build proves the std surface resolves under the wdk-build UMDF link settings
(kernel32 is /NODEFAULTLIB - std must come via OneCoreUAP). If std fails to link
here, the SwapChainProcessor worker-thread design needs a CreateThread shim before
any callback work (port-plan critique gap #9).

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

packaging/windows/drivers/pf-vdisplay/src/lib.rs

@@ -0,0 +1,70 @@
+//! pf-vdisplay — the all-Rust UMDF IddCx virtual-display driver (M1 step-2 rewrite, on wdk-sys + the
+//! owned pf-vdisplay-proto ABI). See docs/windows-host-rewrite.md §14 for the full port plan.
+//!
+//! STEP 0 (this commit): the workspace scaffold + the std-under-UMDF LINK GATE. DriverEntry →
+//! WdfDriverCreate → (EvtDeviceAdd) WdfDeviceCreate, plus a `#[used]` probe that forces `std::thread`
+//! + `OwnedHandle` to link — the SwapChainProcessor (STEP 5) depends on both, and the wdk-build UMDF
+//! link settings `/NODEFAULTLIB:kernel32.lib`, so std must resolve via OneCoreUAP. If this fails to
+//! link, the worker-thread/handle design needs a CreateThread shim BEFORE any callback work (port-plan
+//! critique gap #9). The adapter/monitor/swapchain/IDD-push logic lands in STEP 2-6.
+
+#![allow(non_snake_case, clippy::missing_safety_doc)]
+
+use wdk_sys::{
+    call_unsafe_wdf_function_binding, NTSTATUS, PCUNICODE_STRING, PDRIVER_OBJECT, PWDFDEVICE_INIT,
+    ULONG, WDFDEVICE, WDFDRIVER, WDF_DRIVER_CONFIG, WDF_NO_HANDLE, WDF_NO_OBJECT_ATTRIBUTES,
+};
+
+const STATUS_SUCCESS: NTSTATUS = 0;
+
+/// STEP-0 link gate (port-plan critique #9). Forces `std::thread` + `std::os::windows::io::OwnedHandle`
+/// to be linked into the UMDF cdylib so STEP 0's `cargo build` actually proves the std surface resolves
+/// under the wdk-build link settings (kernel32 is `/NODEFAULTLIB`'d → std must come via OneCoreUAP).
+/// Never called; `#[used]` keeps the symbol so the linker pulls std. Also touches `wdk-iddcx` to prove
+/// the pf-vdisplay → wdk-iddcx → wdk-sys/iddcx dependency graph resolves.
+fn _std_link_gate() {
+    use std::os::windows::io::OwnedHandle;
+    let t = std::thread::spawn(|| 0u32);
+    let _ = t.join();
+    let _drop_owned: fn(OwnedHandle) = core::mem::drop;
+    // touch the iddcx surface via wdk-iddcx (forces the feature-enabled dep graph)
+    let _adapter: Option<wdk_iddcx::iddcx::IDDCX_ADAPTER> = None;
+}
+#[used]
+static _STD_LINK_GATE: fn() = _std_link_gate;
+
+#[unsafe(export_name = "DriverEntry")]
+pub unsafe extern "system" fn driver_entry(
+    driver: PDRIVER_OBJECT,
+    registry_path: PCUNICODE_STRING,
+) -> NTSTATUS {
+    // SAFETY: zeroed then Size + the device-add callback set, per the WDF_DRIVER_CONFIG contract.
+    let mut config: WDF_DRIVER_CONFIG = unsafe { core::mem::zeroed() };
+    config.Size = core::mem::size_of::<WDF_DRIVER_CONFIG>() as ULONG;
+    config.EvtDriverDeviceAdd = Some(evt_device_add);
+    // SAFETY: driver + registry_path are loader-provided; config is valid for the call.
+    unsafe {
+        call_unsafe_wdf_function_binding!(
+            WdfDriverCreate,
+            driver,
+            registry_path,
+            WDF_NO_OBJECT_ATTRIBUTES,
+            &mut config,
+            WDF_NO_HANDLE.cast::<WDFDRIVER>()
+        )
+    }
+}
+
+extern "C" fn evt_device_add(_driver: WDFDRIVER, mut device_init: PWDFDEVICE_INIT) -> NTSTATUS {
+    let mut device: WDFDEVICE = core::ptr::null_mut();
+    // SAFETY: device_init is the framework-provided init; attributes null; device receives the handle.
+    let _ = unsafe {
+        call_unsafe_wdf_function_binding!(
+            WdfDeviceCreate,
+            &mut device_init,
+            WDF_NO_OBJECT_ATTRIBUTES,
+            &mut device
+        )
+    };
+    STATUS_SUCCESS
+}