[haan]

Composite aggregation previously placed its diamond according to the association’s creation direction. Add a Whole (composite) selector so users can choose either connected class.

• Show the whole on the left and the part on the right, with matching header/subtitle ordering and a filled-diamond connector.
• Keep the whole stored as the target by reversing endpoints, endpoint labels, handles, and manual control points in one undoable action. Preserve version 2 file compatibility.
• Keep long dropdown labels within the control, with full names available on hover and in wrapping menu options.
• Update help and regression coverage for selection, reversal, routing, history, and save/reopen behavior.

Validation: 699 unit tests passed; ESLint and the production build passed. Browser visual verification was blocked by the Windows computer-use browser policy limitation.