- Add QmdMemoryBackend class implementing MemoryBackend interface with async agent execution
- Backend executes QMD memory operations via subprocess spawn with configurable command/args
- Graceful fallback to readonly mode on write failures with error logging
- Add readWithoutFetch() and bootstrap() helpers to ProjectMemory for backend-aware read/bootstrap semantics
- Wire QMD backend into TaskStore.create() and memory initialization
- Export QmdMemoryBackend and BackendCapabilities from @fusion/core
- Add comprehensive tests for QMD backend and project memory helpers