feat(windows): AMD (AMF) + Intel (QSV) hardware encode on the Windows host

The Windows host was NVIDIA-only (NVENC) with an openh264 software fallback. Add
AMD AMF and Intel QSV via libavcodec — the Windows analogue of the Linux VAAPI
backend — so one installer serves all three GPU vendors.

- encode/ffmpeg_win.rs: new WinVendor{Amf,Qsv} encoder. System-memory NV12/P010
  readback (default, robust) + opt-in zero-copy D3D11 (PUNKTFUNK_ZEROCOPY: shares
  the capturer's ID3D11Device; AMF takes AV_PIX_FMT_D3D11, QSV derives a QSV frames
  ctx and maps) with a system fallback for the format-group mismatch the capturer's
  video-processor fallback can produce. HDR Main10 (P010 + BT.2020/PQ VUI; an
  Rgb10a2->P010 swscale covers the shader fallback).
- encode.rs: Codec::amf_name/qsv_name; open_video + windows_resolved_backend()
  resolve PUNKTFUNK_ENCODER=auto|nvenc|amf|qsv|sw via a DXGI adapter VendorId probe.
- capture/dxgi.rs: gpu_mode mirrors the resolved backend (D3D11 NV12/P010 for AMF/QSV).
- gamestream/serverinfo.rs: GPU-aware codec advertisement (windows_codec_support;
  AV1 gated to RDNA3+/Arc, like the VAAPI path).
- Cargo.toml: amf-qsv feature (optional ffmpeg-next in the windows target block).
- CI/installer: windows-host.yml sets FFMPEG_DIR + builds --features nvenc,amf-qsv;
  the Inno installer bundles the FFmpeg DLLs; host.env default nvenc -> auto.

CI-green target; AMF/QSV not yet on-glass validated (no AMD/Intel Windows box in the
lab) — NVENC stays live-validated. An adversarial-review pass caught + fixed real
FFI bugs (AV_PIX_FMT_P010 is a macro -> P010LE; windows-rs 0.62 GetImmediateContext/
GetDesc1 return Result; AV_HWFRAME_MAP_* is a bindgen enum with no BitOr).

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

docs/windows-host.md

@@ -143,12 +143,15 @@ rustc 1.96 clippy is stricter than the Linux CI image on shared code, e.g. `need
    driver DLL — `lib /def:nvenc.def /machine:x64 /out:nvencodeapi.lib` where `nvenc.def` lists
    `NvEncodeAPICreateInstance` and `NvEncodeAPIGetMaxSupportedVersion` — and set
    `PUNKTFUNK_NVENC_LIB_DIR` to its directory.
-3. `cargo build -p punktfunk-host --features nvenc` (needs NASM + CMake for aws-lc-rs; libclang for
-   any ffmpeg-using client). Default build (no feature) uses the openh264 software encoder.
+3. `cargo build -p punktfunk-host --features nvenc,amf-qsv` for the all-vendor GPU host (NVENC for
+   NVIDIA; AMD AMF + Intel QSV via libavcodec — `amf-qsv` needs `FFMPEG_DIR` with the `*_amf`/`*_qsv`
+   encoders at build, e.g. the BtbN gpl-shared tree, and the FFmpeg DLLs on PATH at run; NASM + CMake
+   for aws-lc-rs; libclang for ffmpeg-sys-next). Default build (no feature) = openh264 software encoder.
 4. Run in the **interactive session** (not a Session-0 service / not over SSH — SendInput + DXGI
-   Desktop Duplication need a desktop): `serve` or `punktfunk1-host --source virtual`. Set
-   `PUNKTFUNK_ENCODER=nvenc` to select NVENC (the DXGI capturer switches to zero-copy D3D11 output to
-   match). The SudoVDA monitor activates once a real GPU drives WDDM, so capture + NVENC then work.
+   Desktop Duplication need a desktop): `serve` or `punktfunk1-host --source virtual`.
+   `PUNKTFUNK_ENCODER=auto` (default) picks the backend from the GPU vendor — `nvenc`/`amf`/`qsv`/`sw`
+   force one. The DXGI capturer emits zero-copy D3D11 NV12/P010 to match any GPU backend; the SudoVDA
+   monitor activates once a real GPU drives WDDM, so capture + encode then work.
 
 ### Dev loop (this repo → the Windows VM)
 
@@ -224,7 +227,7 @@ This is the highest-value first move and is **fully doable GPU-less**.
 | **VirtualDisplay** | KWin/gamescope/Mutter/Sway | **SudoVDA** IOCTLs (below) + `SetDisplayConfig` mode-set | ✅ likely (WARP) — *spike* |
 | **Capture** | PipeWire/dmabuf | **DXGI Desktop Duplication** primary, **WGC** fallback → `ID3D11Texture2D`; add `FramePayload::D3d11` | ⚠️ DDA-on-WARP unreliable; WGC-on-WARP unverified — *spike* |
 | **Zero-copy** | dmabuf→EGL/Vulkan→CUDA | register `ID3D11Texture2D` with NVENC (`NV_ENC_DEVICE_TYPE_DIRECTX`) — no CUDA bridge | ❌ needs real GPU |
-| **Encode** | ffmpeg `*_nvenc` | `openh264` SW (default on VM) + `nvidia-video-codec-sdk` HW (real GPU); behind `PUNKTFUNK_ENCODER` | SW ✅ / HW ❌ |
+| **Encode** | ffmpeg `*_nvenc`/`*_vaapi` | `nvidia-video-codec-sdk` (NVIDIA) + libavcodec `*_amf`/`*_qsv` (AMD/Intel, `encode/ffmpeg_win.rs`, `--features amf-qsv`) + `openh264` SW fallback; vendor-auto via `PUNKTFUNK_ENCODER` | NVENC ✅ live / AMF/QSV CI-only |
 | **Input kbd/mouse** | libei / wlr | **SendInput** with `MOUSEEVENTF_VIRTUALDESK` absolute mapping onto the virtual desktop rect (skip the VK→evdev table — client sends Win VKs; use `KEYEVENTF_SCANCODE`+`EXTENDEDKEY`) | ✅ |
 | **Gamepad** | uinput xpad + FF | **ViGEmBus** via `vigem-client` (`Xbox360Wired`); rumble via `request_notification()`→`XNotification{large,small}` | ✅ (install driver) |
 | **Audio capture** | PipeWire sink monitor | **WASAPI loopback** via the `wasapi` crate (48 kHz stereo f32 → existing Opus) | ⚠️ needs an audio endpoint |