fix: handle 'no_access' status for Claude-instant (a2) bot

[jishux2]

Description

This PR fixes a bug where the code crashes when attempting to access Claude-instant (a2) bot, which is now private and inaccessible. The current code doesn't handle the no_access status properly, resulting in a TypeError when trying to access attributes of None.

Changes Made

1. Added handling for no_access status in message response
2. Added safety checks before accessing chat data
3. Improved error handling to provide clearer error messages

Additional Notes

The README.md currently uses Claude-instant (a2) in its examples. Since this bot is no longer accessible, it would be helpful to update the examples to use a different bot that's currently available.

Error Details

When trying to access Claude-instant (a2), the API returns:

{
    "data": {
        "messageEdgeCreate": {
            "message": None,
            "status": "no_access",
            "statusMessage": "Claude-instant has been made private by its creator. Your chat history is saved but you won't be able to send new messages to this bot. Try @mentioning another bot."
        }
    }
}

Without proper handling, this leads to:

TypeError: 'NoneType' object is not subscriptable