fix: guard against undefined contentWindow in GiscusComments

[bh462007]

Summary

Fixes #1933

The GiscusComments component sends a postMessage to the giscus iframe whenever colorMode changes. While it already checked if the iframe existed, it didn't verify that the iframe had finished loading.

If colorMode changed before iframe.contentWindow became available, calling postMessage would throw a TypeError.

Fix

Extended the existing guard to ensure both the iframe and its contentWindow are available before sending the message.

if (!iframe || !iframe.contentWindow) {
  return;
}

Testing

• Ran the project locally using npm run start.
• Reproduced the issue with an isolated test where contentWindow was undefined, confirming the Cannot read properties of undefined (reading 'postMessage') error.
• Verified that toggling the theme on blog posts with Giscus comments no longer produces console errors after the fix.

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[github-actions]

✅ Synchronized metadata from Issue #1933:

• Labels: area:UI, roadmap, level 1, recode, Enhacement
• Milestone: recode:live 2.0

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Project	Deployment	Actions	Updated (UTC)
recode-website	Ready	Preview, Comment	Jul 9, 2026 11:45pm