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>

packaging/rpm/punktfunk.spec

@@ -261,7 +261,7 @@ install -Dm0644 web/web.env.example                %{buildroot}%{_datadir}/punkt
 %endif
 
 %files
-%license LICENSE-MIT LICENSE-APACHE
+%license LICENSE-MIT LICENSE-APACHE THIRD-PARTY-NOTICES.txt
 %doc README.md design/implementation-plan.md packaging/README.md
 %{_bindir}/punktfunk-host
 %{_udevrulesdir}/60-punktfunk.rules
@@ -276,7 +276,7 @@ install -Dm0644 web/web.env.example                %{buildroot}%{_datadir}/punkt
 %{_datadir}/%{name}/*
 
 %files client
-%license LICENSE-MIT LICENSE-APACHE
+%license LICENSE-MIT LICENSE-APACHE THIRD-PARTY-NOTICES.txt
 %{_bindir}/punktfunk-client
 %{_datadir}/applications/io.unom.Punktfunk.desktop
 %{_udevrulesdir}/70-punktfunk-client.rules
@@ -284,7 +284,7 @@ install -Dm0644 web/web.env.example                %{buildroot}%{_datadir}/punkt
 
 %if %{with web}
 %files web
-%license LICENSE-MIT LICENSE-APACHE
+%license LICENSE-MIT LICENSE-APACHE THIRD-PARTY-NOTICES.txt
 %{_bindir}/punktfunk-web-server
 %dir %{_datadir}/punktfunk-web
 %{_datadir}/punktfunk-web/.output