feat: add `@aeorank/jekyll` framework plugin

[vinpatel]

Jekyll still powers GitHub Pages and a huge number of developer blogs. A Jekyll plugin would put AEOrank one gem install away for that audience.

Scope

Ship packages/jekyll as either:

• A Jekyll plugin gem (idiomatic) that hooks site.post_write and writes the 9 files to _site/
• Or a standalone CLI step (npx @aeorank/jekyll) that reads _config.yml — simpler, ships first

Either is fine for v1.

Reference

• packages/astro — the simplest existing plugin, ~50 LOC. Copy as template.
• The 9 generators live in packages/core/src/generators/. Just call them with the site config you parse from _config.yml.

Acceptance

• packages/jekyll/ publishes as @aeorank/jekyll
• Installable in 2 lines (either gem install or npm install)
• A test verifies the 9 files are generated against a fixture Jekyll site
• apps/docs gets a /frameworks/jekyll/ page