fix: sub-options are skipped when their parent failed

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KkpbsMw4rQyBsxDG6ebHK2

lib/backend.sh

@@ -185,6 +185,11 @@ backend_apply() {
         if backend_run_component "$c" disable; then feature_record "$c" disable; else failed+=("$c"); fi
     done
     for c in "${TO_ENABLE[@]}"; do
+        # A sub-option of something that just failed isn't applied: it would be left on without its parent.
+        if [[ -n "${PARENT[$c]:-}" && " ${failed[*]:-} " == *" ${PARENT[$c]} "* ]]; then
+            warn "Skipping ${LABEL[$c]%%:*}: ${LABEL[${PARENT[$c]}]%%:*} didn't work."
+            continue
+        fi
         if backend_run_component "$c" enable; then is_action "$c" || feature_record "$c" enable; else failed+=("$c"); fi
     done
     feature_record_unticked