salesforce-misc/byoc-ott-demo-app ? reverse-engineered prompt

Build me a small demo app for testing Salesforce messaging.

I want a page that lets me try inbound and outbound messages, and also attach a file to an inbound message. The app should have a settings panel where I can change things like the conversation channel definition, channel address identifier, end user client identifier, and the custom event field names, then save those changes and use them right away.

On the main messaging side, I want a simple text box to type a message, a Send button, and a file picker for attachments. It should connect to Salesforce using values from a local env file, handle the auth setup, and send the message so I can see it show up in the messaging session record in Salesforce if everything is configured correctly.

Make it run locally on port 3000, with clear setup from a .env file, and keep the interface simple and easy to use. If you need current Salesforce docs while wiring it up, look them up online.