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-link

@@ -38,7 +38,7 @@ target=$(realpath -e "$1" 2>/dev/null) || {
 
 for required in bin default shell; do
   if [[ ! -d "$target/$required" ]]; then
-    echo "Warning: $target/$required not found — does this look like an omarchy-installer checkout?" >&2
+    echo "Warning: $target/$required not found — does this look like an Omarchy source checkout?" >&2
   fi
 done