- Closes#1526 and #1527.
## Type of Change
- [x] Bug fix
- [ ] New feature
- [ ] Breaking change
- [ ] Documentation update
## Motivation and Context
This PR fixes `system df` to report actual on-disk allocated bytes
(content blobs + snapshots) instead of summing per-image snapshot sizes.
Orphaned blobs are now included as reclaimable, and storage shared
across tags is no longer double counted. Also consolidates three
identical `calculateDirectorySize` implementations into a shared
`FileManager.allocatedSize(of:)` extension.
## Testing
- [x] Tested locally
- [x] Added/updated tests
- [ ] Added/updated docs
Raj