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>

clients/windows/packaging/pack-msix.ps1

@@ -67,9 +67,12 @@ $layout = Join-Path $OutDir 'layout'
 if (Test-Path $layout) { Remove-Item -Recurse -Force $layout }
 New-Item -ItemType Directory -Force -Path (Join-Path $layout 'Assets') | Out-Null
 
-# binary + auto-staged runtime bits (reactor stages the App SDK bootstrap DLL + resources.pri,
-# the sdl3 crate stages SDL3.dll — see crate build output).
-$required = @('punktfunk-client.exe', 'Microsoft.WindowsAppRuntime.Bootstrap.dll', 'SDL3.dll', 'resources.pri')
+# binaries + auto-staged runtime bits (reactor stages the App SDK bootstrap DLL + resources.pri,
+# the sdl3 crate stages SDL3.dll — see crate build output). punktfunk-session.exe is the Vulkan
+# session client the shell spawns for every stream (sibling resolution — see clients/windows/
+# src/spawn.rs); Skia links statically and vulkan-1.dll is a GPU-driver component, so the session
+# adds no DLLs of its own.
+$required = @('punktfunk-client.exe', 'punktfunk-session.exe', 'Microsoft.WindowsAppRuntime.Bootstrap.dll', 'SDL3.dll', 'resources.pri')
 foreach ($f in $required) {
     $src = Join-Path $TargetDir $f
     if (-not (Test-Path $src)) { throw "missing build artifact '$f' in $TargetDir (did 'cargo build --release' run?)" }