feat: showRemovedDiffNodes from addDiffToArrayObjs

[jeseed]

add 'diff:removed" to computedNodes

[greptile-apps]

Greptile Summary

This PR enhances Cedar OS's diff tracking system to include removed items in array-based state diffs. Previously, the addDiffToArrayObjs function in useRegisterDiffState.ts only tracked 'added' and 'changed' items, completely omitting removed items from the computed state. The implementation now performs a two-pass operation: first processing added/changed items, then iterating through the old state to identify items not present in the new state and marking them with 'diff:removed'.

The change maintains backward compatibility by preserving the original function signature and return type while extending functionality. To support testing this new feature, a delete button was added to the ProductRoadmapChat component that removes the first node from the current state using Cedar OS's executeStateSetter with the isDiff: true option.

This enhancement completes the diff tracking functionality for array mutations, ensuring all three types of operations (add, change, remove) are captured in the computed state. This is particularly valuable for UI scenarios where users need to visualize what was deleted and potentially restore it, such as in product roadmaps or other data management interfaces. The implementation integrates seamlessly with Cedar OS's existing undo/redo operations and selective change acceptance/rejection system.

Confidence score: 4/5

• This PR is safe to merge with minimal risk as it enhances existing functionality without breaking changes
• Score reflects well-structured implementation with proper error handling and backward compatibility
• Pay close attention to the array iteration logic in useRegisterDiffState.ts to ensure removed items are correctly identified

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