Add real-event frontend histories for grid direction, cell alignment and
justification through main edits, update-main and reset. Check whole-group
override retention, clean children and one-step exact undo/redo for all
thirteen user actions. Compare cells through source identities against
explicit expectations without production assignment helpers.
Register the new namespace in both frontend runner lists.
Validation: focused histories pass 151 assertions; the full frontend suite
passes 1,747 tests and 13,720 assertions. Frontend lint and format pass.
AI-assisted-by: gpt-6
b84411c5c9