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/Cargo.toml

@@ -7,7 +7,7 @@
 # crates/pf-vdisplay-proto from the main tree.
 [workspace]
 resolver = "2"
-members = ["wdk-probe"]
+members = ["wdk-probe", "wdk-iddcx", "pf-vdisplay"]
 
 [workspace.package]
 edition = "2024"
@@ -19,6 +19,7 @@ publish = false
 wdk = "0.4.1"
 wdk-sys = "0.5.1"
 wdk-build = "0.5.1"
+wdk-iddcx = { path = "wdk-iddcx" }
 pf-vdisplay-proto = { path = "../../../crates/pf-vdisplay-proto" }
 
 # Vendored windows-drivers-rs 0.5.1 (the published, self-contained crates) + an added `iddcx`