RFC: Persistent Chat History with Workspace-Based Sessions

## Summary
Proposing to add persistent chat history tied to workspaces/projects, allowing users to continue conversations across terminal sessions.

## Problem
Currently, Amazon Q CLI chat sessions are ephemeral - closing the terminal loses all conversation history. This creates friction for:
- Accidental terminal closure during long troubleshooting sessions
- Project continuity across sessions
- Context switching between multiple projects

## Proposed Solution
- Workspace-based session management
- Automatic session detection and persistence
- Cross-session context integration
- Export/import functionality

## RFC Document
I have prepared a detailed RFC document (~15,000 words) covering:
- Technical architecture
- Database schema design
- User experience flows
- Implementation phases
- Integration with existing codebase

Would the maintainers be interested in reviewing this RFC? I can submit it as a PR once we align on the approach.

## Impact
This addresses a frequently requested feature and would significantly improve the developer experience for complex, multi-session workflows.