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.
