Add LibreTranslator SEO webpage translator template

[dannyward630]

Summary

• Add libretranslator-seo, a Codesphere-ready Node/Express template for SEO-friendly webpage translation with a configurable LibreTranslate-compatible endpoint.
• Add plugin-style language buttons, server-side translation proxy endpoints, in-memory caching, glossary overrides, and translated HTML SEO metadata (hreflang) preview support.
• Include Codesphere ci.yml, template metadata, cover image, README, and a ready-to-publish blog draft.

Issue

Addresses #15.

Notes

The issue asks for an externally published blog article. I included BLOG_DRAFT.md as a publishable draft, but I have not published it externally.

Verification

• rm -rf node_modules && npm ci && npm test
• git diff --check
• Browser smoke with ALLOW_MOCK_TRANSLATION=true PORT=3124 npm start:
  • opened http://localhost:3124
  • DE language button translated marked text in mock mode
  • Build preview returned canonical/alternate hreflang metadata
  • checked desktop and 390px mobile layout snapshots