fix: add nodeRef to CSSTransition for React 19 compatibility

[devin-ai-integration]

Summary

Add nodeRef props to all CSSTransition components to prepare for React 19 compatibility. In React 19, react-transition-group requires explicit nodeRef usage instead of relying on findDOMNode, which has been removed.

Changes:

• Upgrade react-transition-group from ^4.4.2 to ^4.4.5
• Alert.jsx: Import useRef, create nodeRef, pass it to CSSTransition and attach to the <span> child
• Modal.jsx: Add a separate transitionRef (distinct from the existing click-outside ref), pass it to CSSTransition and attach to the <div className={styles.modalContainer}> child

Review & Testing Checklist for Human

• Verify alert toast animations still appear/disappear correctly when guessing words
• Verify modal open/close fade transitions work (e.g. stats modal, settings modal, help modal)
• Confirm click-outside-to-close still works on modals (the existing ref for useOnClickOutside is preserved separately)

Notes

This is Session B of a 4-session parallel migration to React 19. Only Alert.jsx, Modal.jsx, and package.json were modified.

Link to Devin session: https://app.devin.ai/sessions/6eaaa16c52e8448194ccaf82d3c0614a
Requested by: @shahmir-masood

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