feat(blog): create post for v26.3.1

[github-actions]

Creates a new blog post for v26.3.1

Check this workflow's logs at https://github.com/nodejs/nodejs.org/actions/runs/27737057629.

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Project	Deployment	Actions	Updated (UTC)
nodejs-org	Ready	Preview	Jun 18, 2026 4:59am

[cursor]

PR Summary

Low Risk
Documentation-only addition of a standard release announcement page; no application or runtime code changes.

Overview
Adds a new English release blog post at apps/site/pages/en/blog/release/v26.3.1.md announcing Node.js 26.3.1 (Current) as a security release (2026-06-18).

The post documents 11 CVEs (TLS, crypto/WebCrypto, HTTP/HTTP2, DNS/net, permission model, proxy credential redaction) with severity labels, a full commit list (including OpenSSL 3.5.7, undici, and llhttp dependency bumps), platform download links, docs URL, and PGP-signed SHASUMS for v26.3.1 artifacts.

^{Reviewed by Cursor Bugbot for commit d7d5d69. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.71%. Comparing base (2bd5c8d) to head (d7d5d69).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8961      +/-   ##
==========================================
+ Coverage   75.68%   75.71%   +0.03%     
==========================================
  Files         102      102              
  Lines        8676     8676              
  Branches      322      321       -1     
==========================================
+ Hits         6566     6569       +3     
+ Misses       2107     2104       -3     
  Partials        3        3              

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[github-actions]

Lighthouse Results

URL	Performance	Accessibility	Best Practices	SEO	Report
/en	🟢 99	🟢 96	🟢 96	🟢 100	🔗
/en/about	🟢 100	🟢 94	🟢 96	🟠 88	🔗
/en/about/previous-releases	🟢 98	🟢 97	🟢 96	🟢 100	🔗
/en/download	🟢 98	🟢 96	🟠 81	🟢 100	🔗
/en/download/archive/current	🟢 100	🟢 97	🟢 100	🟢 100	🔗
/en/blog	🟢 100	🟢 97	🟢 96	🟢 100	🔗