Fix HTML markup issues and owlCarousel autoplay runtime error

[tobibako45]

Motivation

• Prevent an owlCarousel2 runtime error caused by an undefined auto variable and fix several small HTML markup issues affecting accessibility and layout.

Description

• Replace autoPlay: auto with autoPlay: true in js/main.js to ensure the carousel autoplay setting is valid.
• Correct two <sapn> typos to valid <span> elements in index.html to fix broken markup.
• Remove an unintended empty <li> from the friends list to normalize the list structure.
• Add rel="noopener noreferrer" to external links that use target="_blank" to improve security.

Testing

• Ran git diff -- js/main.js index.html to review changes and it completed successfully.
• Searched for remaining occurrences with rg -n "sapn|autoPlay: auto|target=\"_blank\"" index.html js/main.js and found no remaining issues, which succeeded.
• Committed the changes with git commit -m "Fix markup issues and carousel autoplay config" and the commit succeeded.
• Created the PR using the PR tool and the PR title/body were recorded successfully.

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Codex Task