feat(clients/windows): port the Vulkan session client to Windows — session-always

The punktfunk-session Vulkan client (clients/linux-session, now clients/session)
builds and runs on Windows; the WinUI shell spawns it for every stream. Verified
live: 10-bit HEVC via Vulkan Video on both AMD (iGPU) and NVIDIA, 5120x1440 at
130 fps / 8 ms end-to-end on the RTX 4090.

- pf-ffvk: Windows bindgen branch (FFMPEG_DIR + PF_FFVK_VULKAN_INCLUDE, no
  pkg-config); provisioning fetches Vulkan-Headers (pinned v1.4.309).
- pf-client-core: builds on Windows — WASAPI audio (audio_wasapi.rs, cfg-swapped
  via #[path], same surface as the PipeWire twin), VAAPI/dmabuf gated inline
  (chain = vulkan -> software), trust reads the WinUI shell's %APPDATA% stores
  (parity tests pin both serialized shapes), Settings gains adapter/hdr_enabled
  (serde-defaulted; Linux stores unaffected).
- pf-presenter: builds on Windows — dmabuf module Linux-gated; SDL keyboard grab
  while captured (Alt+Tab/Win reach the host); pick_device ranks discrete over
  integrated (device 0 was the iGPU on hybrid boxes — the silent footgun) and
  honors PUNKTFUNK_VK_ADAPTER (the Settings GPU pick, exported by the session).
- run loop: block in one SDL wait woken by input AND decoded frames (a per-
  session forwarder pushes a FrameWake user event) instead of a 1 ms poll —
  measured 111%% -> 5%% of a core (NVIDIA), 86%% -> 3.5%% (AMD), stats unchanged.
  The pump's decode-fence wait became once-per-window sampling (no per-frame
  pipeline stall; the stat now shows true backlog).
- pf-console-ui: builds on Windows (skia-safe msvc prebuilts); font lookup falls
  through fontconfig aliases to concrete DirectWrite families (Consolas/Segoe UI)
  — browse/coverflow works, verified against a live host.
- WinUI shell: session-always via new src/spawn.rs (GTK spawn.rs port —
  CREATE_NO_WINDOW, stdout contract, kill handle); the Stream screen is a status
  card (chips + stage lines from the child's stats). The legacy in-process
  D3D11VA path stays behind Settings "Streaming engine" / PUNKTFUNK_BUILTIN_
  STREAM=1 as the A/B baseline until Phase 8 deletes it. SessionParams.video_caps
  makes the HDR toggle real.
- clients/linux-session renamed to clients/session (builds for both OSes).
- CI/MSIX: both workflows build/test both bins with widened path filters; the
  MSIX ships punktfunk-session.exe. ARM64 session builds --no-default-features
  (rust-skia has no aarch64-pc-windows-msvc prebuilts; flip when it does).

A/B on this box (5120x1440 HEVC vs home-worker-5): NVIDIA Vulkan 130 fps / 8 ms
e2e / 1.6 ms decode — clearly better than the built-in path. The AMD iGPU VCN
saturates at ~52 fps where its own D3D11VA does ~70 — Adrenalin Vulkan decode is
slower on APU silicon; discrete RDNA validation gates Phase 8.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/pf-client-core/src/lib.rs

@@ -1,26 +1,37 @@
-//! Shared, UI-agnostic Linux-client plumbing, extracted verbatim from the GTK client
+//! Shared, UI-agnostic client plumbing, extracted verbatim from the GTK client
 //! (design: punktfunk-planning `linux-client-rearchitecture.md`, Phase 0) so the desktop
-//! shell and the Vulkan session binary build on one implementation.
+//! shells and the Vulkan session binary build on one implementation — on Linux AND
+//! Windows (the session binary runs on both; macOS stays `wol`-only, clients/apple is
+//! the client there).
 //!
 //! Nothing here may depend on a UI toolkit: the presenter contract is `session`'s
-//! channels (`SessionHandle`) and `video`'s `DecodedImage` (RGBA bytes or dmabuf fds +
-//! plane layout) — how frames reach the screen is the consumer's business.
+//! channels (`SessionHandle`) and `video`'s `DecodedImage` (RGBA bytes, dmabuf fds +
+//! plane layout, or a decoded VkImage) — how frames reach the screen is the consumer's
+//! business.
+//!
+//! Audio is the one per-OS module swap: `audio.rs` (PipeWire) on Linux,
+//! `audio_wasapi.rs` (WASAPI) on Windows — same public surface, picked here by `#[path]`
+//! so `crate::audio` is the only name the session pump ever sees. `keymap` (evdev-keyed)
+//! stays Linux: the session path uses pf-presenter's SDL-scancode table instead.
 
 #[cfg(target_os = "linux")]
 pub mod audio;
-#[cfg(target_os = "linux")]
+#[cfg(windows)]
+#[path = "audio_wasapi.rs"]
+pub mod audio;
+#[cfg(any(target_os = "linux", windows))]
 pub mod discovery;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", windows))]
 pub mod gamepad;
 #[cfg(target_os = "linux")]
 pub mod keymap;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", windows))]
 pub mod library;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", windows))]
 pub mod session;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", windows))]
 pub mod trust;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", windows))]
 pub mod video;
 
 pub mod wol;