Remove footer link spacing and darken text

[Llewellynvdm]

Summary

• remove the 5px sibling margin from footer directory links in portable and YOOtheme markup
• render directory links with Montserrat 500 at full-opacity #2d2e33
• load the real Montserrat 500 face in the portable document head and example
• update the footer/typography/source documentation and reusable-agent contract
• regenerate the distributable CSS and extend validation for the corrected footer contract

Verification

• npm run check passes
• generated CSS is synchronized with src/css/footer.css
• protected logo, favicon, skyline, and social assets are unchanged

The supplied before/after screenshots establish the zero-margin, darker-text footer as the owner-approved reference.