Fix broken anchor and wrong image path in index.html

[Copilot]

Two errors in index.html causing a broken link and a missing profile photo.

Changes

• Malformed anchor (line 52): Unquoted href, no link text, and </a> accidentally embedded in the URL as a literal /a> suffix. Quoted the attribute, stripped the spurious /a from the URL, and added link text.

  <!-- Before -->
  <a href=https://doi.org/10.31222/osf.io/c4xwg_v1/a></strong>
  
  <!-- After -->
  <a href="https://doi.org/10.31222/osf.io/c4xwg_v1">this link</a></strong>

• Wrong image path (line 123): Niko Busch's photo referenced css/200niko_busch_400px.jpg — that directory contains only stylesheets. Changed to images/200niko_busch_400px.jpg where the file actually lives.

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