Add DigiDollar integration guide link to digibyte.org

[DennisPitallano]

Summary

Add a link to the new DigiDollar integration guide on digibyte.org so developers, exchanges, and wallet providers can find the official document for integrating DigiByte's native USD-pegged stablecoin into their services.

Background

DigiDollar is being introduced as a native USD-pegged stablecoin on the DigiByte blockchain. A wallet menu entry for "DigiDollar" already ships in the DigiByte Core Qt wallet and links to https://digibyte.io/digidollar, but the public site (digibyte.org) currently has no entry point to the integration guide alongside the existing Integration guide, Info paper, and Media sheet resources.

Proposed change

Mirror the existing "Integration guide" pattern on every locale index.html (root + 35 locale folders) and add the DigiDollar guide in three places:

1. Hero CTA pill — new "DigiDollar guide" pill next to the existing "Integration guide" pill.
2. "DigiByte Documents & Guides" slick slider — new slide between the Integration guide and Media sheet slides.
3. Footer "Resources" list — new <li> directly under "DGB Integration Guide".

All three link to docs/DigiDollar_integration_guide.pdf. The slider tile uses images/digibyte_symbol_06c.svg as the avatar.

Notes

• Labels are in English across all locales for the initial rollout; translated copy can land in a follow-up.
• The en/index.html JS-only redirect stub is not modified.
• A PR with the implementation is open against this repo.