fix(graphing): keep label input focused while it is being edited PIE-681

[PatriciaRomaniuc]

In ibx, the focus of the labels was lost when the model was auto saving.

• Each tool now tracks editingLabel in state ('from'/'to'/'middle', point index, or 'label') and passes it down as autoFocus;
• MarkLabel focuses itself in an effect keyed on [autoFocus, input, disabled], so a remount re-acquires focus. It also keeps the caret at the end (setSelectionRange) instead of dropping it to position 0, skips the prop→state sync while it holds focus, and reports onBlur upward so the tool clears editingLabel. Each tool additionally clears editingLabel in componentDidUpdate when label mode is left.
• Debounce went 200ms → 500ms as DEBOUNCE_DELAY.
  https://illuminate.atlassian.net/browse/PIE-681