[improvement] Clearly mark Chat as Beta and explain how it works

Users may not realize that the Chat feature is still in beta, which can lead to confusion or incorrect expectations.

We’ve added clear indicators and explanations to improve transparency and trust.

Goal:

• Show a visible “Beta” badge in the Chat header

• Provide a clear explanation via the info icon

• Set expectations about accuracy and ongoing improvements

• Communicate that all processing is private and happens on-device