Deleted character chats do not lock creator studio or input

Issue

When a character is deleted, existing chats with that character remain accessible but the creator studio and chat input are not properly locked.

Steps to Reproduce

1. Create a character
2. Start a chat with it
3. Delete the character
4. Open the chat — you can still see it, but creator studio and input are not locked as they should be

Expected Behavior

• Chats should remain viewable (so users can export if needed)
• Creator studio should be locked for deleted characters
• Chat input should be disabled for deleted characters

Context

Reported by LuDeRu. Related concern: if a creator deletes all their characters in a crash-out moment, existing chats break entirely. Users should at least be able to export their chat history before everything stops working.