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>

packaging/windows/pack-host-installer.ps1

@@ -25,6 +25,7 @@ param(
     [string]$Publisher = 'CN=unom',
     [string]$PfxBase64 = $env:MSIX_CERT_PFX_B64,                    # reuse the client's signing secret
     [string]$PfxPassword = $env:MSIX_CERT_PASSWORD,
+    [string]$FfmpegDir = $env:FFMPEG_DIR,                           # bundle its bin\*.dll (amf-qsv build)
     [switch]$NoDriver,                                              # build without the bundled SudoVDA driver
     [switch]$NoSign                                                 # skip signing (local debug)
 )
@@ -146,6 +147,24 @@ if (-not $NoDriver) {
 }
 else { Write-Host "-NoDriver: building installer WITHOUT the bundled SudoVDA driver" }
 
+# --- stage the FFmpeg shared DLLs (AMD/Intel AMF/QSV build) ------------------------------------
+# A host built with --features amf-qsv link-imports avcodec/avutil/swscale/... so the shared DLLs
+# MUST sit next to the exe (it won't start otherwise). Bundle them from $FfmpegDir\bin — the same
+# BtbN gpl-shared tree the build linked against. A nvenc/software-only build doesn't import them, so
+# this is a harmless extra there; skipped entirely when $FfmpegDir is unset.
+$ffmpegBinSrc = if ($FfmpegDir) { Join-Path $FfmpegDir 'bin' } else { $null }
+if ($ffmpegBinSrc -and (Test-Path $ffmpegBinSrc)) {
+    $dlls = Get-ChildItem -Path $ffmpegBinSrc -Filter '*.dll' -ErrorAction SilentlyContinue
+    if ($dlls) {
+        $ffmpegStage = Join-Path $OutDir 'ffmpeg'
+        New-Item -ItemType Directory -Force -Path $ffmpegStage | Out-Null
+        $dlls | ForEach-Object { Copy-Item $_.FullName -Destination $ffmpegStage -Force }
+        $defines += "/DFfmpegBin=$ffmpegStage"
+        Write-Host "bundling $($dlls.Count) FFmpeg DLL(s) from $ffmpegBinSrc"
+    }
+}
+else { Write-Host "no FFMPEG_DIR\bin -> installer built WITHOUT FFmpeg DLLs (nvenc/software-only host)" }
+
 # --- build the installer (from the non-redirected copy under C:\t) -----------------------------
 Write-Host "==> ISCC $($defines -join ' ') $issLocal"
 & $iscc @defines $issLocal

packaging/windows/punktfunk-host.iss

@@ -32,6 +32,11 @@
 #ifdef StageDir
   #define WithDriver
 #endif
+; FfmpegBin (a dir of FFmpeg shared DLLs) is optional — present when the host is built with
+; --features amf-qsv (the AMD/Intel AMF/QSV encode backend link-imports the FFmpeg libs).
+#ifdef FfmpegBin
+  #define WithFfmpeg
+#endif
 
 [Setup]
 AppId={{7C9E6A52-1F4B-4E8D-A3C7-2B5D8F1E0A93}
@@ -68,6 +73,12 @@ Name: "startservice"; Description: "Start the punktfunk host service now (also s
 Source: "{#BinDir}\punktfunk-host.exe"; DestDir: "{app}"; Flags: ignoreversion
 Source: "{#HostEnv}"; DestDir: "{app}"; Flags: ignoreversion
 Source: "{#Readme}"; DestDir: "{app}"; DestName: "README.txt"; Flags: ignoreversion
+#ifdef WithFfmpeg
+; FFmpeg shared DLLs (avcodec/avutil/swscale/...) laid down next to the exe — the AMD/Intel
+; (AMF/QSV) encode backend link-imports them, so the exe won't start without them. NVENC/software-
+; only builds simply omit this block.
+Source: "{#FfmpegBin}\*.dll"; DestDir: "{app}"; Flags: ignoreversion
+#endif
 #ifdef WithDriver
 ; The driver payload + nefconc.exe + install-sudovda.ps1, extracted to {tmp} and removed after install.
 Source: "{#StageDir}\*"; DestDir: "{tmp}\sudovda"; Flags: deleteafterinstall recursesubdirs createallsubdirs; Tasks: installdriver