Fix link checker accepted status codes and base URL

[Zhengyizhe0209-arch]

Summary

This pull request updates the link checker configuration used by the scheduled workflow.

In issue #734, many successful 200 OK responses are reported as rejected status codes. This appears to be related to the current --accept 403,503 setting, which is too restrictive for normal successful HTTP responses.

The report also includes errors for root-relative links such as /_notebooks/... and /_pdf/..., which cannot be converted into URLs when checking local HTML files. This PR adds a base URL so that these links can be resolved against the deployed site.

Changes

• Accept normal successful HTTP responses with 200..=299.
• Keep the existing accepted 403 and 503 status codes.
• Add --base-url https://intro.quantecon.org to resolve root-relative links.

Addresses #734.

[netlify]

✅ Deploy Preview for taupe-gaufre-c4e660 ready!

Name	Link
🔨 Latest commit	227ea0c
🔍 Latest deploy log	https://app.netlify.com/projects/taupe-gaufre-c4e660/deploys/6a0c3dedf21ddc00082f0554
😎 Deploy Preview	https://deploy-preview-736--taupe-gaufre-c4e660.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

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

[Copilot]

Pull request overview

This PR updates the scheduled link-checking workflow configuration to (1) treat normal successful HTTP responses as acceptable and (2) correctly resolve root-relative links found in locally checked HTML files by providing a deployment base URL.

Changes:

• Expand accepted HTTP status codes to include 200..=299 (while keeping 403 and 503).
• Add --base-url https://intro.quantecon.org so root-relative links (e.g., /_pdf/...) can be resolved during checks.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mmcky]

Thanks for the contribution, @Zhengyizhe0209-arch! 👋

I had a look and this is a real fix, not a workaround:

• --accept 200..=299,403,503: lychee's --accept replaces the default accepted set rather than adding to it, so the previous --accept 403,503 was inadvertently rejecting every 200 OK. The report in Link Checker Report #734 confirms this verbatim (Rejected status code: 200 OK (configurable with "accept" option)). Restoring 2xx is the correct fix.
• --base-url https://intro.quantecon.org: the /_notebooks/... and /_pdf/... entries weren't broken — lychee couldn't construct a URL to check them at all. The base URL lets it resolve and actually verify them against the deployed site, which is strictly more checking than before.

LGTM 👍 — happy to merge. The next scheduled run (or a manual workflow_dispatch) should produce a much smaller, more honest report, and we can triage any genuine breakage from there.