Add 'timestamp' to last-updated documentation pages

[devin-ai-integration]

Summary

Updates terminology in two documentation pages related to the last-updated frontmatter property, replacing "message" and "dates" with "timestamp" for consistency and better findability:

• frontmatter.mdx: Changed "Displays a 'Last updated' message" → "Displays a 'Last updated' timestamp"
• auto-update-last-updated.mdx: Changed "Last updated dates accurate" → "Last updated timestamp accurate"

Review & Testing Checklist for Human

• Verify "timestamp" is the intended terminology for these pages
• Check preview links to confirm pages render correctly

Notes

Requested by Fern Support ([email protected])

Link to Devin run

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[github-actions]

🌿 Preview your docs: https://fern-preview-485efdb3-cd9f-420b-b468-0583c221bd91.docs.buildwithfern.com/learn