feat(host/windows): DXGI Desktop Duplication capture backend

Windows Capturer via DXGI Desktop Duplication: create a D3D11 device on the SudoVDA adapter (by LUID), find the matching output (by GDI name), DuplicateOutput, and per AcquireNextFrame copy the desktop into a CPU-readable staging texture -> tightly-packed BGRA (FramePayload::Cpu, feeds the openh264 software encoder GPU-lessly). Handles WAIT_TIMEOUT (reuse last frame) and ACCESS_LOST (re-duplicate). Adds FramePayload::D3d11(D3d11Frame) for the future NVENC zero-copy path, and a VirtualOutput.win_capture identity (adapter LUID + GDI name) carried out of the SudoVDA backend. Pure helpers (pack_luid/gdi_name_matches/depad_bgra) unit-tested on the VM; the live duplication path needs a real GPU + an activated SudoVDA monitor. Compiles clean on Windows + Linux.

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

crates/punktfunk-host/src/vdisplay/sudovda.rs

@@ -281,6 +281,10 @@ impl VirtualDisplay for SudoVdaDisplay {
         Ok(VirtualOutput {
             node_id: 0, // unused on Windows; the capture target is the GDI name below
             preferred_mode: Some((mode.width, mode.height, mode.refresh_hz)),
+            win_capture: gdi_name.clone().map(|n| crate::capture::dxgi::WinCaptureTarget {
+                adapter_luid: crate::capture::dxgi::pack_luid(ao.luid),
+                gdi_name: n,
+            }),
             keepalive: Box::new(SudoVdaKeepalive {
                 device: device_raw,
                 guid: MONITOR_GUID,