feat: add -DryRun flag for preview-only mode

[Diwak4r]

Overview

Add a -DryRun switch parameter that scans all target paths and reports what WOULD be cleaned and how much space WOULD be freed, without deleting anything.

Implementation

1. Add [switch] DryRun to the param() block
2. In Remove-FolderContents and Remove-PathContents, skip Remove-Item when DryRun is set
3. Change Write-Status prefix to [DRY] in dry-run mode
4. Update summary to say Estimated space savings
5. Update Show-Banner to show a yellow DRY RUN MODE indicator

Effort

~30 minutes.