feat: taxonomy catch-alls, scan/migrate fixes, and tag recall/FP benchmarks

feat: expand taxonomy funnel with act, fallback, and Voyeur sub-folders

feat: add nested Voyeur soft taxonomy with theme precedence

feat: improve taxonomy routing and restore scaled media sampling

Implement destination folder validation in migrate_run function. Add checks to ensure the destination folder exists and is a directory, with appropriate error handling and logging for failed migrations. This enhances the robustness of the migration process by preventing invalid paths from causing issues.