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.

bin/omarchy-dev-pkg-test

@@ -11,7 +11,7 @@ if [[ ${1:-} == "-h" || ${1:-} == "--help" ]]; then
   cat <<USAGE
 Usage: omarchy dev pkg-test [package-name] [path-to-checkout]
 
-Builds and installs an Omarchy package from a local omarchy-installer
+Builds and installs an Omarchy package from a local Omarchy source
 checkout. Use when changes need to land at fixed system paths (/etc/,
 /usr/lib/systemd/, udev rule bodies, plymouth) that omarchy-dev-link
 can't shadow.