fix: add missing Jekyll gems for docs build

- Add jekyll-include-cache (required by just-the-docs theme)
- Add faraday-retry (recommended for Faraday v2.0+ support)

Fixes: Jekyll build failure on GitHub Actions for docs deployment

Author: RecurPixel

docs/Gemfile

@@ -5,3 +5,5 @@ gem "jekyll-remote-theme"
 gem "jekyll-github-metadata"
 gem "jekyll-seo-tag"
 gem "jekyll-relative-links"
+gem "jekyll-include-cache"
+gem "faraday-retry"