Add unit tests for TypewriterText

[barney-w]

Summary

TypewriterText at packages/agent/src/streaming/TypewriterText/TypewriterText.tsx has no tests.

What to do

1. Create packages/agent/src/streaming/TypewriterText/__tests__/TypewriterText.test.tsx
2. Use vitest + @testing-library/react + vi.useFakeTimers()
3. Test cases to include:
   • Text renders progressively (characters appear over time)
   • onComplete callback fires when the animation finishes
   • Cursor is hidden when showCursor={false}
   • Cursor disappears after completion
   • An axe accessibility check passes

Useful references

• Component: packages/agent/src/streaming/TypewriterText/TypewriterText.tsx
• Test pattern to follow: packages/core/src/inputs/TextArea/__tests__/TextArea.test.tsx
• Test tooling: vitest, @testing-library/react, vitest-axe