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.

test/cli

@@ -135,9 +135,6 @@ assert_output_contains "bare share help uses canonical route" "$output" "omarchy
 output=$("$CLI" menu share)
 assert_output_contains "bare required-arg filename route renders CLI help" "$output" "omarchy share <clipboard|file|folder> [path...]"
 
-output=$("$CLI" branch set)
-assert_output_contains "bare required-choice route renders CLI help" "$output" "omarchy branch set <master|rc|dev>"
-
 CLI="$CLI" python3 <<'PY'
 import json
 import os