[AnVIL DX] Update content for guides documentation

[frano-m]

Summary

Review and update the content for the AnVIL Data Explorer guides documentation pages:

• /guides — About AnVIL Explorer (overview)
• /guides/data-download-options — Data Download Options
• /guides/tsv-file-manifest-download — TSV File Manifest Download
• /guides/data-download-via-curl — Data Download via curl
• /guides/individual-file-download — Individual File Download

Tasks

• Review guide content for accuracy and completeness
• Update screenshots if UI has changed
• Ensure all links are valid and up to date
• Verify content matches current application behavior