chore(licensing): LGPL FFmpeg swap, third-party notices, attribution hygiene

The MIT OR Apache-2.0 SOURCE license is clean (audit found no copied copyleft); the
gaps were all binary-distribution (Layer-2). This makes the shipped artifacts honest:

- Windows host + client: bundled FFmpeg BtbN gpl-shared -> lgpl-shared (AMF/QSV/decode
  unaffected; the GPL-only x264/x265 were never used), and ship the FFmpeg LGPL notice
  + license text in the installer + MSIX (licenses/).
- THIRD-PARTY-NOTICES.txt generated + bundled into installer/MSIX/deb/rpm. Offline
  generator (scripts/gen-third-party-notices.{py,sh}) + cargo-about config (about.toml/
  .hbs) with a permissive-only accepted-license allow-list as a copyleft regression gate.
- Reword the win32u GPU-preference hook comments to reflect independent reimplementation
  (no Apollo/Sunshine GPL-3.0 source copied).
- README dual-license + inbound=outbound contributor clause + non-affiliation trademark
  disclaimer; new CONTRIBUTING.md.
- LICENSE files into the standalone driver + vk-layer workspaces; deb copyright holder
  aligned to "unom and the punktfunk contributors".

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

.gitea/workflows/windows-host.yml

@@ -24,8 +24,9 @@
 # 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
+#  - AMF/QSV (AMD/Intel, libavcodec): link-imports the FFmpeg libs from FFMPEG_DIR (the BtbN lgpl-shared
 #    tree the client uses; includes the *_amf/*_qsv encoders) and bundles its DLLs into the installer.
+#    lgpl-shared (not gpl-shared) keeps those bundled DLLs LGPL (we never use the GPL-only x264/x265).
 # CI never launches the exe, so no GPU is needed here — this is build + Windows clippy coverage only.
 name: windows-host
 
@@ -80,7 +81,7 @@ 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
+          # FFMPEG_DIR: the same BtbN lgpl-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.