docs: add licensing and compliance documentation

Add comprehensive FOSS compliance documentation including:
- COPYRIGHT.md: copyright holders and code ownership
- LICENSING.md: GPL-3.0-or-later policy and source offer
- NOTICE: attribution requirements for permissive licenses
- THIRD-PARTY-LICENSES.md: third-party software inventory
- TRADEMARKS.md: trademark notices and non-affiliation
- os-release hook and files: identify FWS as separate from Arch Linux

These documents establish legal compliance baseline for GPL/AGPL/Apache/MIT/BSD obligations before public distribution.

configs/releng/airootfs/etc/pacman.d/hooks/zz-fws-os-release.hook

@@ -0,0 +1,20 @@
+# remove from airootfs!
+# Branding FWS : le paquet « filesystem » d'Arch installe /usr/lib/os-release
+# avec NAME="Arch Linux". On le remplace par la version FWS APRÈS l'installation
+# des paquets (PostTransaction), donc sans conflit pacman « exists in filesystem »
+# (poser le fichier dans l'overlay déclencherait ce conflit, cf. ordre overlay→
+# pacstrap dans mkarchiso). /etc/os-release reste un lien vers ce fichier.
+# Ce hook ne sert qu'au build : zzzz99-remove-custom-hooks le retire du système.
+
+[Trigger]
+Operation = Install
+Operation = Upgrade
+Type = Package
+Target = filesystem
+
+[Action]
+Description = Applying FWS branding to /usr/lib/os-release...
+When = PostTransaction
+Depends = filesystem
+Depends = coreutils
+Exec = /usr/bin/install -Dm0644 /usr/local/share/fws/os-release /usr/lib/os-release