feat: misc improvements for LLM verification

[ellvix]

• If you switch browsers (or clear cookies), the system no longer knows you're verified.
• Switch from js prompt to more modern popup
• After Verify, you must hit Save and Close to lock it in. They probably won't know this. We either need explanation text, or better yet to do it automatically.
• If user is verified, we need to hide user keys. Maybe add a radio input to switch between verified email and U IL, and user API keys
• Add Enter trigger verification, as that's what users do
• Once verified, make email field read only (to make it clear they're locked in), remove Verify button, and have a delete button instead