feat(har): port date filter and dry-run summary improvements from legacy hc - #73

Summary

Ports the date-based file filtering feature and dry-run output improvements from the legacy hc CLI into the unified harness CLI migration module.

Date filter (AH-4341, AH-4458, AH-4518):

• Adds DateFilter config block per registry mapping — createdAfter / downloadedAfter with ANY / ALL match logic
• Queries JFrog via AQL (POST /artifactory/api/search/aql) to get per-file timestamps, then narrows the file list before tree construction
• For PYTHON (atomic version artifacts), threads an unfilteredRoot through the job chain so all distribution files for a version are migrated if any single file is within the date window
• DryRunStats mutations are now protected by a mutex — fixes concurrent map write panics (AH-4458)

Dry-run summary (AH-4430):

• Tally loop now counts registries → packages → versions → files from the directory tree
• For OCI types (DOCKER/HELM) with no versioned file entries, falls back to totalPackages with label "Total packages (filtered):" instead of the raw source file count
• Nil guards added at all three nesting levels in the tally loop
• Two pterm.Info console messages added during filtering: pulled file count and skip count