feat(host/windows): WGC capture backend (overlay/HDR-correct) with watchdog'd DDA fallback

The capture-architecture reset from the research: add a Windows.Graphics.Capture (WGC) backend that
captures the COMPOSED desktop — including the overlay/independent-flip/MPO planes DXGI Desktop
Duplication misses — which structurally fixes the frozen HDR animations + video (proven live: a WGC
frame decodes to the real 5120x1440 HDR content DDA freezes on). It reuses the whole pipeline
unchanged: the WGC frame's GPU texture → same scRGB→BT.2020-PQ shader → NVENC zero-copy; the OS
composites the cursor (IsCursorCaptureEnabled) so no manual cursor pass. crates/punktfunk-host/src/
capture/wgc.rs; find_output/make_device/HdrConverter/nudge_cursor_onto made pub(crate) for reuse.

Reliability findings + mitigations (live on the RTX 4090):
- WGC can't activate under the SYSTEM account (0x80070424) — it needs the interactive user token. The
  host must run as the user for WGC (run.cmd: drop PsExec -s). DDA still needs SYSTEM for the secure
  desktop — that token reconciliation (impersonation) is the remaining task.
- WGC's Direct3D11CaptureFramePool::CreateFreeThreaded intermittently HANGS on the headless SudoVDA
  (IddCx) display, correlated with accumulated SudoVDA churn (failed REMOVEs leaving lingering
  displays); clean-state opens reliably. Since it's a blocking hang, capture_virtual_output runs WGC
  open on a watchdog thread with a 5s timeout and falls back to DDA on hang/error — the session is
  NEVER left black: WGC when it opens (fixed animations), DDA otherwise. First-frame nudge added (WGC
  fires FrameArrived on change; a static desktop otherwise never delivers the first frame).
- Default WGC; PUNKTFUNK_CAPTURE=dda forces DDA. DDA path unchanged.

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

crates/punktfunk-host/Cargo.toml

@@ -126,6 +126,14 @@ windows = { version = "0.62", features = [
     "Win32_Graphics_Direct3D11",
     "Win32_Graphics_Direct3D_Fxc",
     "Win32_Graphics_Gdi",
+    # Windows.Graphics.Capture (WGC) backend — composed-desktop capture (overlay/MPO-correct HDR).
+    "Foundation",
+    "Graphics",
+    "Graphics_Capture",
+    "Graphics_DirectX",
+    "Graphics_DirectX_Direct3D11",
+    "Win32_System_WinRT_Direct3D11",
+    "Win32_System_WinRT_Graphics_Capture",
 ] }
 # Software H.264 encoder (GPU-less path + NVENC fallback). The default `source` feature statically
 # compiles OpenH264 (BSD-2) — no system lib, builds on MSVC; nasm on PATH adds the SIMD fast path.