Fix search engine page indexing and structured data issues

[jacamera]

See Google Search Console for details.

Page indexing issues detected in readup.org:

• Duplicate without user-selected canonical
• Page with redirect
• Excluded by ‘noindex’ tag
• Soft 404
• Server error (5xx)

Review snippets structured data issues detected in readup.org:

• Invalid object type for field "itemReviewed"
• Missing field "ratingValue"
• Value in property "ratingCount" must be positive
• Value in property "reviewCount" must be positive