Add SFTP storage and integration tests#13

Menelion merged 20 commits into

masterOire/sharp-sync:masterfrom

claude/analyze-storage-implementations-011CUu4KwE4bXVUUcGzDHdLDOire/sharp-sync:claude/analyze-storage-implementations-011CUu4KwE4bXVUUcGzDHdLDCopy head branch name to clipboard