Add optional filename field to export dialog with automatic .json
extension handling. Extract resolveFilename() for testability. Add
tests for includeHistory flag, bundleToJson, and filename resolution.
Add export format compatibility note to CLAUDE.md.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Add export dialog with download/clipboard options and optional
undo/redo history inclusion (default off). Extract shared Dialog
component to ui/dialog.tsx, consolidating open/close lifecycle,
backdrop click, and escape key handling from all 6 dialog components.
Update spec to reflect export method dialog and optional history.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
