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/session/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+name = "punktfunk-client-session"
+description = "punktfunk/1 Vulkan session binary — SDL3 window, ash presenter, terminal stats; the power-user / gamescope stream client"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+authors.workspace = true
+repository.workspace = true
+
+[[bin]]
+name = "punktfunk-session"
+path = "src/main.rs"
+
+[features]
+default = ["ui"]
+# The Skia console UI (stats OSD, capture HUD, later the gamepad library). Dropping it
+# (`--no-default-features`) is the ~15 MB-smaller power-user build: same streaming,
+# stats on stdout only.
+ui = ["dep:pf-console-ui", "dep:serde_json"]
+
+# Same Linux+Windows gating as the rest of the client stack; elsewhere this is a stub
+# binary.
+[target.'cfg(any(target_os = "linux", windows))'.dependencies]
+pf-presenter = { path = "../../crates/pf-presenter" }
+pf-console-ui = { path = "../../crates/pf-console-ui", optional = true }
+pf-client-core = { path = "../../crates/pf-client-core" }
+punktfunk-core = { path = "../../crates/punktfunk-core", features = ["quic"] }
+# The fake-library dev hook (`PUNKTFUNK_FAKE_LIBRARY`, browse mode) parses GameEntry JSON.
+serde_json = { version = "1", optional = true }
+anyhow = "1"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }