Class AutoFixLayout

AutoFixLayout performs best-effort layout corrections on a diagram in three ordered passes:

1. Autoconnect dangling connections whose loose endpoint is within CONNECT_THRESHOLD of exactly one non-connection node.
2. Align nodes whose shared edges fall within an alignment threshold (±4 px by default).
3. Equalize spacing for node groups that already share an axis and are near-uniform in spread.

All mutations are covered by a single addUndo() call, giving the user one undo entry.