Reliable Undo and Safer Branch Editing

🔄 Improvements

• Improved branch reparenting accuracy with a larger drop zone for more precise control when moving branches

🛠 Fixes

• Fixed: Undo for child branch reordering now works in a single step and matches the visible order
• Fixed: Undo for branch notes now removes or restores the note on the first press
• Fixed: Undo after moving a branch now correctly restores it instead of breaking the structure Video
• Fixed: Undo for branch color changes now works per click instead of grouping multiple changes Video
• Fixed: Undo for in-place branch movement now correctly restores the previous position Video
• Fixed: Large attachment uploads no longer crash the server when parsing data URLs
• Fixed: Debug overlay no longer disappears or crashes during branch movement

And other improvements