Input box issues

[nirgranthi]

• When the model is thinking, Enter key shouldn't stop the model. Only stop button is supposed to stop the model.

• When the model is thinking, Enter key should replace the last user message.

• Make the placeholder dynamic

• Stop and Send button should change color in a gradient

• Add new-line support on Shift+Enter

• Add multi-line support

[nirgranthi]

f45ede5 Fixed: Add new-line support on Shift+Enter