Use JS for updating height of the Chat Input control

[hellovolcano]

Pull Request

🤨 Rationale

The Spright Chat Input is currently pulled in to an application that's being hosted in CEF 119.4.3, which does not yet have support for field-sizing as described in this bug. The long-term fix is to upgrade CEF, but we need a fix in the next few weeks before that upgrade can happen.

👩‍💻 Implementation

Use JavaScript to measure textarea's scrollHeight, compute 6-line max from resolved line-height and add padding to set the text area's inline height on when the user is adding text/resizing the text area.

Once content exceeds that max height, the logic switches the textarea to overflowY = 'auto'; otherwise it keeps overflowY = 'hidden', and it separately recalculates scrollbar width so the error icon placement stays correct when a vertical scrollbar appears.

🧪 Testing

• Manual validation (confirmed problematic behavior in Firefox (since that property is also not supported there). Used Storybook to manually test control grows and shrinks during expected user actions.
• Tests passing

✅ Checklist

• I have updated the project documentation to reflect my changes or determined no changes are needed.