fix: Auto-select first target option in Combine Groups

The target group listbox (size > 1) wasn't auto-selecting an option,
causing targetGroupSelect.value to be empty and parseInt('') to return
NaN, silently failing the combine operation.

Also adds e2e tests for Combine Groups feature and ignores .claude/commands/

Author: malston

.gitignore

@@ -41,3 +41,4 @@ dist/
 .serena/
 .worktrees/
 .claude/settings.local.json
+.claude/commands/