Function buildMenuItems

Recursive menu-item builder shared by ContextMenuManager and MainMenuManager.

• Walks items depth-first, allocating a new id from state.nextId++ for each leaf command.
• Maps each allocated id to the identifier state.family can actually dispatch, inside state.idMap, so callers can later dispatch via ExecuteByID. Items offering no such identifier stay unmapped.
• Stops once state.limit is hit (when set).

Pure function: never mutates the input items.