Make setup ISO-only

Remove legacy online installer entrypoints, collapse migrations for 4.0, and move setup responsibilities into target-side system, hardware, and user commands.

install/post-install/dns-resolver.sh

@@ -0,0 +1,5 @@
+# https://wiki.archlinux.org/title/Systemd-resolved
+# The target does not need the stub file to exist yet; systemd-resolved creates
+# it at boot.
+echo "Symlinking resolved stub-resolv to /etc/resolv.conf"
+ln -sf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf