refactor: switch from FTPS/lftp to rsync for deployment

Replace the FTPS-based deployment approach with rsync over SSH for more
reliable and efficient mirroring of the Hugo site. This change addresses
issues with the previous approach and provides true mirror behavior.

Key changes:
- Replace lftp with rsync for file synchronization
- Add --delete flag for true mirror behavior (removes stale remote files)
- Simplify authentication to use SSH keys only (no password needed)
- Update all documentation and OpenSpec artifacts
- Add .envrc to gitignore for direnv users

Environment variables:
- SSH_USER: SSH username (required)
- SSH_HOST: server hostname (required)
- SSH_PORT: SSH port (optional, defaults to 22)
- REMOTE_ROOT: remote directory path (optional, defaults to /httpsdocs)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitignore

@@ -36,3 +36,4 @@ package-lock.json
 .env
 .env.*
 !.env.example
+.envrc