Per-Chat System Prompt Persistence

Current Behavior:

System prompts are applied globally. Changing the system prompt in one chat affects all chats, including existing ones that were created under a different system prompt.

Problem:

If a user sets a specific system prompt for Chat A, then creates Chat B with a different system prompt, returning to Chat A reverts it to whichever system prompt was last set. This makes it impossible to maintain distinct system prompts across separate conversations.

Requested Behavior:

System prompts should be saved per-chat rather than globally. Once a system prompt is set for a specific chat, it should persist for that chat regardless of system prompt changes made in other chats.