Refactor and Enhance Chat Input Box Behavior (Medium)

**Description:**

Update the chat interface input box to improve usability and prevent inconsistent behavior:

**Requirements:**

Auto-Resize Behavior:

- When the user presses Shift + Enter, the input box expands for a new line.
- However, if the added whitespace is deleted, the input should automatically collapse back to its original height.

Disable Manual Resizing:

- Remove or disable the draggable resizer (bottom-right corner) to prevent manual resizing of the input box.

Prevent Empty Message Submission:

- Disable the send functionality when the input box is empty or contains only whitespace.

Disable Input During Processing:

- When a message is being processed/sent, disable the input box and prevent the user from typing or submitting another message until the current message is complete.

Update Send Button UI:

- Replace the current "Send" button with an arrow image icon to better reflect the chat interaction.