feat(blog): recreate article footer navigation and related posts

- add reusable live-site-faithful blog footer component
- extract previous, next, and related post data from article content
- remove duplicated footer fragments from multilingual articles
- document the repeatable footer extraction workflow

www/src/content/blog/en/aba-school-readiness-arizona.mdx

@@ -161,25 +161,3 @@ If your child is between the ages of 2 and 6 and could benefit from a program th
   }
 ]}
 />
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-###### [Positive Reinforcement in ABA Therapy to Encourage Skill Development](positive-reinforcement-techniques)
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-###### [Autism and Fall Break: How to Keep Routines Calm and Predictable](autism-fall-break-routine-tips-halloween-thanksgiving)
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