fix(links): use /schemas path + exclude iec.ch from lychee

[ronaldtse]

Summary

Clean up the remaining 3 link-checker errors from the Astro migration in #22.

• /schemas.html to /schemas in src/content/pages/about.mdx and src/components/islands/HomePage.vue. Astro generates pretty directory-style URLs (/schemas/index.html), so the .html suffix produced "File not found" for lychee.
• Exclude https://www.iec.ch/* from lychee. The IEC site returns 403 Forbidden to automated user agents (it works fine for real browsers) — same category as the existing ibm.com / grantadesign.com / babcockinternational.com / unf.edu exclusions.

Test plan

• Link Checker workflow passes after merge
• Site builds + deploys — already working from fix(ci): point workflows at dist/ (Astro output, not .vitepress/dist) #23

Follow-up to #22 and #23. Please merge with rebase-merge.

[github-actions]

🔗 Link Check Failed

Results

Summary

Status	Count
🔍 Total	681
🔗 Unique	110
✅ Successful	675
⏳ Timeouts	0
🔀 Redirected	4
👻 Excluded	4
❓ Unknown	0
🚫 Errors	2
⛔ Unsupported	0

Errors per input

Errors in dist/about/index.html

• [415] http://www.xml-cml.org/ (at 48:1930) | Rejected status code: 415 Unsupported Media Type

Errors in dist/supporters/index.html

• [415] http://www.xml-cml.org/ (at 68:12) | Rejected status code: 415 Unsupported Media Type

Redirects per input

Redirects in dist/about/index.html

• https://3docx.org/ --[307]--> https://3docx.org/en/
• https://www.bipm.org/ --[302]--> https://www.bipm.org/en/

Redirects in dist/supporters/index.html

• https://3docx.org/ --[307]--> https://3docx.org/en/
• https://www.bipm.org/ --[302]--> https://www.bipm.org/en/

Full Github Actions output