Plan step 12, containment.md C-04. `with-close-button` defaulted to
false, so a drawer could render with no exit at all once
`close-on-escape` and the scrim were off. It now defaults to true, and
`:with-close-button="false"` is ignored where nothing else closes the
sheet: Escape off, the scrim off, or a pane, which has neither.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
