feat(windows-host): OutputFormat into the capturer — kill the dxgi back-reference (Goal-1 stage 5, tightening 1)

The headline §2.3 seam tightening (the explicit Stage-3 deferral; §5's "highest-severity
coupling"): the capturer is now TOLD its output format instead of re-deriving the encode backend.

New `capture::OutputFormat { gpu, hdr }`, resolved once per session and passed INTO
capture_virtual_output:
  * native punktfunk/1 path: `SessionPlan::output_format()` (gpu = encoder.is_gpu(), from the
    already-resolved plan.encoder — no second probe; hdr = plan.hdr).
  * GameStream + spike paths: `OutputFormat::resolve(hdr)` (gpu from the single `gpu_encode()`
    source, which maps windows_resolved_backend()).

`capture/dxgi.rs DuplCapturer::open` takes `gpu` in and its internal
`!matches!(windows_resolved_backend(), Software)` recompute is DELETED — the capture layer no
longer re-calls the encode layer (the back-reference that could let capture and encode disagree
on whether frames are GPU-resident, plan §2.3/§5). The relay's secure-desktop DDA passes
`gpu_encode()` likewise.

Behavior-preserving: the `gpu` passed in equals the value the capturer used to compute (same
encode-backend resolution). The DDA opens keep `want_hdr=false` (the SDR fallback, unchanged).

Tightenings 2 (HDR/release -> VirtualLease) and 3 (EncoderCaps) split off: (2) needs the
monitor-generation carried on the lease + the keepalive becoming Box<dyn VirtualLease> — that's
the §2.5 ownership-model change (CURRENT_MON_GEN / sudovda::wait_for_monitor_released), so it
moves there; (3) is a small additive follow-on. Documented in the plan.

Verified: Linux cargo check + clippy (-D warnings) + fmt clean. Box build to follow.

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

crates/punktfunk-host/src/punktfunk1.rs

@@ -2715,6 +2715,9 @@ fn virtual_stream_relay(ctx: SessionContext) -> Result<()> {
                 target.clone(),
                 Some((w, h, hz)),
                 Box::new(()),
+                // The relay's host encoder is GPU (NVENC/AMF/QSV unless software) — pass `gpu` in (Goal-1
+                // stage 5) so the DDA capturer doesn't re-derive it.
+                crate::capture::gpu_encode(),
                 hdr,
             )
             .context("open DDA for secure desktop")?;
@@ -3140,8 +3143,9 @@ fn build_pipeline(
     // VIDEO_CAP_10BIT + host opted in via PUNKTFUNK_10BIT) is our HDR path → BT.2020 PQ Rgb10a2;
     // otherwise the FP16 IDD frames are converted to 8-bit SDR. (Ignored by non-IDD-push backends,
     // which auto-detect HDR from the monitor state.)
-    let mut capturer = crate::capture::capture_virtual_output(vout, plan.hdr, plan.capture)
-        .context("capture virtual output")?;
+    let mut capturer =
+        crate::capture::capture_virtual_output(vout, plan.output_format(), plan.capture)
+            .context("capture virtual output")?;
     capturer.set_active(true);
     let frame = capturer.next_frame().context("first frame")?;
     // `bit_depth` is the handshake-negotiated value (8, or 10 = HEVC Main10 when the client