Copy entire chats & Rollback chats to certain message

[peerschuett]

• Added a way to copy an entire chat. The copy opens right away so you can continue in it, while the original conversation stays exactly as it was.
• Added a way to roll a chat back to an earlier AI response. The response you pick stays, and every message after it is removed permanently, together with the attachments of those messages.
• Added a rollback that leaves your draft alone: whatever you have typed and attached below the message field is still there afterwards, ready for you to continue.
• Added a safeguard to the rollback: when a chat has already seen confidential data, it keeps demanding the same trust of every provider you continue it with, even after you remove the messages that brought that data in.