feat: scaffold Arcline OS build system

Scaffold the Arcline OS build system ("the wires"): a transparent,
auditable pipeline that turns a Debian bookworm base into hardened OS
images for the server, workstation, and cloud editions.

- Makefile orchestrates everything (make iso-<edition>, check, test,
  toolchain, clean); versions.mk is the single source of truth for
  versions and paths.
- scripts/ is the plain-bash pipeline: debootstrap -> install packages
  -> apply overlays -> in-chroot configure -> live ISO, plus a rootfs
  archive along the way.
- ARCLINE_TOOLCHAIN=auto|skip|require controls whether the 11 Go tools
  are bundled into an image (auto by default; minimal builds available
  via make iso-<edition>-minimal).
- GPL-3.0 licensed, sponsored by Arcline IT LLC.

.gitignore

@@ -0,0 +1,18 @@
+# Build artifacts
+build/
+*.iso
+*.tar.xz
+*.deb
+*.log
+
+# Toolchain output
+toolchain/out/
+
+# Local mirrors / caches
+.cache/
+mirror/
+
+# Editor cruft
+*.swp
+*~
+.DS_Store