Add preview branch audit mode and batch reporting

[arberx]

Summary

• Add batch audit flows for local previews, sitemap crawls, changed routes, and compare mode
• Extend CLI, workflow, and config handling for preview-safe targets, retries, thresholds, and critical pages
• Improve content extractability scoring for script-heavy pages and add batch-friendly text and markdown output

Testing

• Added and updated unit tests for fetch validation, changed-page discovery, sitemap handling, config parsing, and content extractability
• Not run (not requested)