063c0a589f
- Phase 1.2: Add SSH_FXP_WRITE data preview (first 20 bytes) - Phase 1.3: Add SSH_FXP_ATTRS serialization debug log (flags, size, permissions, etc.) - Improve SFTP debugging capability for future troubleshooting - Reference: OpenSSH sftp-server.c logging style Changes: - sftp_handler.rs: handle_write() - add data preview debug log - sftp_handler.rs: SftpAttrs::serialize() - add detailed field log