- Add MemoryBackend interface with file and QMD backend implementations
- Implement QMD memory backend with async execution, atomic writes, and fallback to file backend
- Add ProjectMemory class with backend-aware read/bootstrap semantics and conflict resolution
- Wire dashboard memory routes to use backend abstraction instead of direct file I/O
- Add comprehensive tests for memory backend and project memory classes
- Update settings reference and architecture docs for new backend configuration
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