feat(utils): safely parse front matter date in readLastUpdateData (Fixes #5691)

[ameerhmz]

Description

Fixes #5691 by ensuring invalid date strings in front matter last_update.date / date are safely handled in readLastUpdateData without propagating NaN timestamps or breaking VCS fallback lookups.

Changes

1. Safely validate parsed timestamp via Number.isNaN(parsedDate) in packages/docusaurus-utils/src/lastUpdateUtils.ts.
2. Added unit test handles invalid date string in front matter gracefully in packages/docusaurus-utils/src/__tests__/lastUpdateUtils.test.ts.

Test Plan

• Added unit test covering invalid front matter date strings.

[meta-cla]

Hi @ameerhmz!

Thank you for your pull request and welcome to our community.

Action Required

In order to merge any pull request (code, docs, etc.), we require contributors to sign our Contributor License Agreement, and we don't seem to have one on file for you.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at cla@meta.com. Thanks!

[netlify]

✅ [V2]

Built without sensitive environment variables

Name	Link
🔨 Latest commit	6cdc15f
🔍 Latest deploy log	https://app.netlify.com/projects/docusaurus-2/deploys/6a79e833bb7ddd00087fa3ab
😎 Deploy Preview	https://deploy-preview-12355--docusaurus-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[meta-cla]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Meta Open Source project. Thanks!