phsl / new-api

The “Batch Create” secret-key input in Channel Edit previously used a TextArea
with a hard-coded `minHeight`, which caused an extra scrollbar and blank space
on the right side of the field.
This change:

• Removes the fixed `minHeight` in favour of `autosize={{ minRows: 6, maxRows: 6 }}`
• Keeps the field’s rounded appearance while letting it grow/shrink with
  content, improving usability on both desktop and mobile

No other components or global styles are affected.