refactor(host/W6.2): extract the shared frame/format vocabulary into the pf-frame leaf crate

The captured-frame types both capture (producer) and encode (consumer) speak —
PixelFormat, OutputFormat, CursorOverlay, CapturedFrame, FramePayload,
DmabufFrame, drm_fourcc — move into crates/pf-frame, alongside the small pure
helpers that ride the same seam: hdr (HDR static metadata / in-band SEI),
metronome (the metronomic-stall detector), thread_qos (per-thread scheduling
QoS), session_tuning (Windows process tuning), and the Windows DXGI capture
IDENTITY (WinCaptureTarget, D3d11Frame, pack_luid, make_device + the GPU
scheduling-priority hardening it applies) (plan §W6).

This is the crate that breaks the capture<->encode cycle: FramePayload's GPU
variants own their backends from BELOW (Cuda -> pf_zerocopy::DeviceBuffer,
D3d11 -> dxgi::D3d11Frame), so encode can speak the vocabulary without a path to
capture, and vice versa. The Windows DXGI identity moving here lets capture,
encode, and pf-vdisplay share ONE WinCaptureTarget/device factory instead of the
old capture<->encode<->vdisplay reach-in.

The host keeps thin facades: capture.rs re-exports the vocabulary
(crate::capture::{PixelFormat,…} unchanged); capture/windows/dxgi.rs keeps the
win32u GPU-preference hook + HDR/video-engine converters + self-test and
re-exports the identity; native.rs re-exports boost_thread_priority from
pf_frame. crate::hdr/metronome/session_tuning callers rewired to pf_frame::*.
metronome's Metronome::new gained a Default impl (new_without_default fires once
the type is public across the crate boundary).

Verified: Linux clippy -D warnings (pf-frame --all-targets + host
nvenc,vulkan-encode,pyrowave --all-targets) + 9/9 pf-frame tests; Windows clippy
nvenc,amf-qsv --all-targets Finished exit 0.

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

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

@@ -1020,8 +1020,8 @@ pub(super) fn virtual_stream(ctx: SessionContext) -> Result<()> {
     // opening GOP, instead of answering it with a redundant second IDR.
     let mut last_forced_idr: Option<std::time::Instant> = Some(std::time::Instant::now());
     // Self-diagnosis for the periodic-stutter class: warns when the served recovery IDRs settle
-    // into a stable multi-second rhythm (see [`crate::metronome::Metronome`]).
-    let mut recovery_cadence = crate::metronome::Metronome::new();
+    // into a stable multi-second rhythm (see [`pf_frame::metronome::Metronome`]).
+    let mut recovery_cadence = pf_frame::metronome::Metronome::new();
     // Position within the current intra-refresh wave (frames since the last IDR/wave start). Only
     // meaningful on a `caps().intra_refresh_recovery` encoder; the pump tags every wave-boundary AU
     // with `USER_FLAG_RECOVERY_POINT` so the client can lift its post-loss freeze on a clean