Rundeck 6's AsyncImportService expects explicit directory entries (with trailing /)
in project archives. Without them, directories like "jobs" extract as zero-byte files,
causing "Not a directory" errors during import.

Changes:
- Collect all parent directories from file paths
- Create JarEntry objects with trailing / for each directory
- Write directory entries before file entries, ordered shallow-to-deep
- Normalize paths to use forward slashes

This ensures archives are compatible with both Rundeck 5 and 6 import mechanisms.