Chat input appears disabled without OpenAI key but lacks user facing explanation

[ShirleyRex]

Summary
When no OpenAI API key is provided, the chat input does not highlight or allow typing. This is a good guardrail, but there is no visible message explaining why the input is disabled. This can feel like a UI bug to new users.

Steps to reproduce

• Open assertify.io in a fresh session.
• Ensure no OpenAI API key is set.
• Navigate to the chat feature.
• Try to click into the chat input and type.

Actual behavior

• The chat input appears inactive and does not highlight.
• No message, tooltip, banner, or inline hint explains that an OpenAI API key is required.

Expected behavior

• The chat input should clearly communicate why it is disabled.
• The UI should guide the user to the next step, such as adding an API key.

Acceptance criteria

• When the OpenAI API key is missing, the chat input stays disabled.
• A clear message is shown near the input explaining why it is disabled.
• The message points to the correct place to add the API key.