There's probably a bit too much JS for such a site. Is the "challenge" necessary? It will limit the amount of browsers the site will work on.
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But I would implement a "if landscape, then present list of titles on a left pane, with <a href='#pos'> page positional links to the right pane article stubs" (no JS needed).
This was a fun little project, but unfortunately can't spend too much time on it. It's also quite expensive to run -- around $15 per day in Gemini summaries (I'm sure 2.5 Flash would be much cheaper, but unsure about the quality)!
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But I would implement a "if landscape, then present list of titles on a left pane, with <a href='#pos'> page positional links to the right pane article stubs" (no JS needed).