Add --no-open boolean flag to both commands via citty's built-in
boolean negation (--no-open sets args.open to false).
- preview.ts: guard all 4 open() calls with args.open check
- play.ts: guard the open() call with args.open check
- Default is true (open browser), preserving existing behavior
Closes#1
Co-authored-by: AnoKno <122017492+AnoKno@users.noreply.github.com>