Add locale configuration, systemd service for rootfs mounting, and customization script:
- Add locale.gen to generate en_US.UTF-8 locale required by Anaconda
- Add fws-rootfsbase.service to expose squashfs as /run/rootfsbase for Anaconda LiveOS payload detection
- Add customize_airootfs.sh to run locale-gen during image build
- Add python-iso639 0.1.4 PKGBUILD (local package with correct find() API)
- Add python-langtable 0.0.71 PKGBUILD (local package with list_common_languages())
- Remove python-iso639 and python-langtable from AUR packages due to version/API incompatibilities
- Update LOCAL_BUILD_ORDER to include new local packages
