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>

.gitea/workflows/windows-host.yml

@@ -20,9 +20,12 @@
 # an ephemeral self-signed cert is generated and its public .cer published next to the installer
 # (import once to LocalMachine\TrustedPublisher). See packaging/windows/pack-host-installer.ps1.
 #
-# NVENC: the host builds with --features nvenc; the only link need is nvencodeapi.lib, synthesised
-# from a 2-export .def with llvm-dlltool (no GPU/SDK at build time). The resulting exe is NVIDIA-only
-# by design — CI never launches it, so no GPU is needed here.
+# GPU backends: the host builds with --features nvenc,amf-qsv = all three vendors in one installer.
+#  - NVENC (NVIDIA, direct SDK): the only link need is nvencodeapi.lib, synthesised from a 2-export
+#    .def with llvm-dlltool (no GPU/SDK at build time).
+#  - AMF/QSV (AMD/Intel, libavcodec): link-imports the FFmpeg libs from FFMPEG_DIR (the BtbN gpl-shared
+#    tree the client uses; includes the *_amf/*_qsv encoders) and bundles its DLLs into the installer.
+# CI never launches the exe, so no GPU is needed here — this is build + Windows clippy coverage only.
 name: windows-host
 
 on:
@@ -59,6 +62,13 @@ jobs:
           # (pwsh Out-File utf8 = no BOM, unlike Windows PowerShell 5.1 — keeps the first line clean).
           "CARGO_TARGET_DIR=C:\t" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
           "CARGO_WORKSPACE_DIR=$env:GITHUB_WORKSPACE" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
+          # FFMPEG_DIR: the same BtbN gpl-shared x64 tree the Windows CLIENT links against (provisioned
+          # by scripts/ci/setup-windows-runner.ps1). The host's AMD/Intel AMF/QSV encode backend
+          # (--features amf-qsv) link-imports avcodec/avutil/swscale from it; pack-host-installer.ps1
+          # then bundles its bin\*.dll into the installer. LIBCLANG_PATH is in the runner daemon env.
+          if (-not $env:FFMPEG_DIR) {
+            "FFMPEG_DIR=C:\Users\Public\ffmpeg" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
+          }
           $v = if ($env:GITHUB_REF -like 'refs/tags/v*') {
             $env:GITHUB_REF_NAME -replace '^v', ''
           } else {
@@ -74,14 +84,15 @@ jobs:
           & packaging/windows/nvenc/gen-nvenc-importlib.ps1 -OutDir C:\t\nvenc
           "PUNKTFUNK_NVENC_LIB_DIR=C:\t\nvenc" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
 
-      - name: Build (release, nvenc)
+      - name: Build (release, nvenc + amf-qsv)
         shell: pwsh
-        run: cargo build --release -p punktfunk-host --features nvenc
+        # All-vendor host: NVENC (NVIDIA, direct SDK) + AMF/QSV (AMD/Intel, libavcodec via FFMPEG_DIR).
+        run: cargo build --release -p punktfunk-host --features nvenc,amf-qsv
 
       - name: Clippy (host, Windows)
         shell: pwsh
         # First-ever Windows lint coverage for the host (Linux CI never lints the windows-cfg code).
-        run: cargo clippy -p punktfunk-host --features nvenc -- -D warnings
+        run: cargo clippy -p punktfunk-host --features nvenc,amf-qsv -- -D warnings
 
       - name: Ensure Inno Setup
         shell: pwsh