feat(build): add podman container support for non-arch linux distributions

Add automatic detection and relaunching of build scripts in an Arch Linux container via podman when running on non-Arch distributions (Fedora, Ubuntu, Debian, etc.).

Key changes:
- Implement host_is_arch() function to detect if running on Arch Linux by checking both pacman availability and /etc/os-release
- When non-Arch host is detected, scripts automatically pull docker.io/library/archlinux:latest and relaunch themselves in rootful podman container with --privileged
- Mount repository at same absolute path inside container so WORK_DIR and out/ directories work transparently
- Set up persistent pacman cache volume (fws-pacman-cache) between runs
- Auto-chown output files back to host user after build completes
- Update pacman config to disable landlock sandbox in containers (similar to WSL workaround)
- Run full pacman -Syu upgrade in container before installing archiso to avoid partial upgrade issues
- Add comprehensive documentation in README about Fedora/non-Arch setup
- Update .gitignore to exclude pkgbuilds/ directory
- Add environnement.md documentation file

configs/baseline/packages.x86_64

@@ -94,12 +94,6 @@ xorg-xsetroot
 openbox
 ttf-dejavu
 
-# --- Bureau FWS installé ---
-xfce4
-xfce4-goodies
-lightdm
-lightdm-gtk-greeter
-
 # --- Agents VM (pratique pour tester l'ISO) ---
 qemu-guest-agent
 virtualbox-guest-utils-nox

configs/releng/packages.x86_64

@@ -93,12 +93,6 @@ xorg-xsetroot
 openbox
 ttf-dejavu
 
-# --- Bureau FWS installé ---
-xfce4
-xfce4-goodies
-lightdm
-lightdm-gtk-greeter
-
 # --- Agents VM (pratique pour tester l'ISO) ---
 qemu-guest-agent
 virtualbox-guest-utils-nox