Complete archiso/Calamares profile scaffold (iso/)

- Calamares modules: unpackfs (clone), partition/mount/fstab (btrfs subvols),
  bootloader (systemd-boot + quiet splash), packages (strip live), services
  (greetd), shellprocess (snapper, flathub, strip-live), branding (Fuji)
- bootstrap-profile.sh: releng base + linux-zen swap + overlay our deltas
- BUILD.md: build steps, decisions, and honest open items (needs build-test)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

iso/overrides/airootfs/etc/calamares/modules/shellprocess-striplive.conf

@@ -0,0 +1,11 @@
+---
+dontChroot: false
+timeout: 30
+# Remove the live-only installer bits from the installed target so it boots the
+# desktop (greetd) instead of auto-launching Calamares.
+script:
+- "rm -f /etc/systemd/system/getty@tty1.service.d/autologin.conf"
+- "rmdir --ignore-fail-on-non-empty /etc/systemd/system/getty@tty1.service.d 2>/dev/null || true"
+- "rm -f /root/.bash_profile"
+- "rm -f /usr/local/bin/tanin-installer"
+- "systemctl set-default graphical.target"