feat(windows): pf-vdisplay IDD-push — HDR + pipelined zero-copy capture

HDR (display-driven, matching the WGC path):
- CTA-861.3 HDR EDID (BT.2020 primaries + HDR Static Metadata block) so Windows
  offers "Use HDR" on the virtual display. The host FOLLOWS the display's live
  advanced-color state, recreating the shared ring at the matching format
  (FP16 in HDR / BGRA in SDR) on a toggle — no freeze.
- Always emit Main10/BT.2020-PQ Rgb10a2 while the display is HDR; the client
  auto-detects PQ from the HEVC VUI (clients under-report VIDEO_CAP_10BIT).
  Generic HDR10 mastering SEI on every IDR.
- Generation-tagged `latest` (gen<<40|seq<<8|slot) + driver `is_stale` re-attach
  kill the toggle-time garbage frame and any stale-ring read.

Perf:
- Pipeline the encode loop (Capturer::pipeline_depth; IDD-push = 2): submit N+1
  before polling N so the convert/copy on the 3D engine overlaps the NVENC encode
  of N on the ASIC. PUNKTFUNK_IDD_DEPTH overrides (1 = synchronous).
- Rotating host output ring (OUT_RING) so the in-flight encode and the next
  convert never touch the same texture.
- HDR converts directly from the keyed-mutex slot's SRV into the output ring
  (drops the redundant slot->fp16 scratch copy); SDR copies the BGRA slot in.
  The slot mutex is held only across the convert/copy, not the encode.
  RING_LEN 3->6 for publish headroom.
- Capture-health diagnostic: new_fps vs repeat_fps under PUNKTFUNK_PERF (a low
  new_fps at a high send rate means the source isn't compositing, not an encode
  stall).

Validated live on the RTX box: 5120x1440@240 HDR streams; driver composes
~180 new fps, encode 240 fps @ ~4.3 ms p50.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/punktfunk-host/src/gamestream/stream.rs

@@ -127,8 +127,15 @@ fn run(
                 refresh_hz: cfg.fps,
             })
             .context("create virtual output at client resolution")?;
+        // `want_hdr=false`: the IDD-push backend (opt-in PUNKTFUNK_IDD_PUSH) has no monitor-HDR
+        // auto-detection — it converts its always-FP16 ring per this flag — and GameStream HDR is not
+        // negotiated into StreamConfig here, so an IDD-push GameStream session streams SDR even on an
+        // HDR desktop. (The default WGC backend DOES auto-detect HDR from the output colorspace, but
+        // IDD-push bypasses WGC.) Acceptable for the experimental IDD-push A/B path; HDR over IDD-push
+        // is wired only for punktfunk/1 (want_hdr = negotiated bit_depth >= 10). TODO: derive want_hdr
+        // from a GameStream HDR flag once StreamConfig carries one.
         let mut capturer =
-            capture::capture_virtual_output(vout).context("capture virtual output")?;
+            capture::capture_virtual_output(vout, false).context("capture virtual output")?;
         capturer.set_active(true);
         return stream_body(&mut *capturer, &sock, cfg, running, force_idr, rfi_range);
     }