Conversation Limit Warning + Auto-Summary for Continuation

PROBLEM:
When a conversation reaches the context window limit, the session ends
abruptly without any prior warning. This is especially frustrating for
premium paid users who expect a reliable and seamless experience.
There is currently no indication of how close a conversation is to
hitting its limit, leaving users with no opportunity to save their
progress or prepare for a new session.

PROPOSED SOLUTION:
1. PROGRESS INDICATOR
   Display a visible usage indicator (e.g. a progress bar or percentage)
   showing how much of the conversation limit has been consumed.
   This should be visible at all times during an active conversation.

2. PROACTIVE WARNINGS
   Notify the user at key thresholds (e.g. 75%, 90%) with a clear
   message such as:
   "You are approaching your conversation limit. We recommend
   saving a summary to continue seamlessly in a new chat."

3. AUTO-SUMMARY + COPY FEATURE
   When the limit is near (or reached), the AI should automatically
   generate a concise, accurate summary of the entire conversation.
   This summary should be:
   - Displayed clearly to the user
   - Easy to copy with a single click ("Copy Summary" button)
   - Formatted so it can be pasted into a new chat as a
     continuation prompt

4. ONE-CLICK "SAVE & CONTINUE" BUTTON
   A dedicated button that:
   - Generates the summary
   - Copies it to the clipboard
   - Opens a new chat window
   - Pre-populates it with the summary so the user can continue
     without interruption

5. LOCAL CONVERSATION HISTORY (OPTIONAL ENHANCEMENT)
   Allow users to optionally save conversation summaries or full
   transcripts locally on their device (not on the server), keeping
   data private and in line with Brave's core privacy values.
   Users should be able to browse past saved conversations and
   reload a summary to resume from where they left off.

WHY THIS MATTERS:
- Premium users are paying for a reliable experience. Being cut off
  without warning is a poor user experience that does not reflect
  the quality expected of a paid tier.
- This feature respects Brave's privacy-first philosophy by keeping
  saved history on-device rather than on servers.
- It reduces server memory usage by encouraging clean session
  handoffs rather than indefinitely long conversations.
- It empowers users to maintain continuity across sessions without
  relying on the server to store their full history.

PRIORITY SUGGESTION: High (especially for Premium tier users) but can be for everyone