Allow configurable memory storage path

Currently the memory system hardcodes ~/.claude/projects/<project>/memory/ as the storage path. There's no way to override this to store memories in the project repo itself (e.g. .claude/memory/).

Storing memories in the repo is useful for:

• Sharing project-specific memories across machines
• Version-controlling memories alongside the codebase
• Keeping all project context in one place

Request: add a memory_path setting (in settings.json or CLAUDE.md) that lets users specify an alternative memory directory, with higher priority than the default user-profile path.