Change chat input from <input> to <textarea> so multi-line messages
are supported. Enter (without Shift) still sends; Shift+Enter inserts
a newline via the native textarea behavior.
- Replace <input> with <textarea rows={1}> in Chat.tsx
- Update onKeyDown: guard sendMessage() with !e.shiftKey check
and call e.preventDefault() to suppress the default newline on Enter
- Update inputRef type from HTMLInputElement to HTMLTextAreaElement
- Add style props: resize:none, overflowY:auto, fontFamily:inherit
- Add 3 new Vitest tests covering all 3 acceptance criteria (AC1-AC3)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
17e9599334