Per-cell undo / redo

• Edit any cell, commit it, then press Cmd+Z — the value reverts and a new commit fires with source: "undo".
• Press Cmd+Shift+Z to redo.
• Edit the SAME row 3 times, then undo 3 times. The stack walks backwards through that row only.
• Edit a different row — the undo stack is per-row, so this row keeps its own history.

• Per-row scope.Each row maintains its own undo stack. Cmd+Z on row A undoes A's most recent commit, not row B's. Matches Excel / Google Sheets convention.
• Capped at 10 entries per row. When the cap is reached, the oldest entry shifts out. Bounds memory regardless of how aggressively a single row is edited.
• Redo stack clears on new commits. Typing a new value invalidates pending redos — the user has chosen a new history branch.
• No-op while editing.If an editor is currently mounted, Cmd+Z is the input's native undo (in-progress text), not the grid's.

When the grid restores a value, it fires onCellEditCommit with source: "undo" or source: "redo". Most consumers can treat undo/redo identically to a normal commit. Branch on event.source if you need to skip secondary side-effects (audit log entry, collaborator notification) that the original commit already triggered.