Render newlines in error messages as <br> instead of literal \n

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/error.html

@@ -8,7 +8,7 @@
     <div class="col-md-7">
       <div class="alert alert-danger">
         <h4 class="alert-heading">Something went wrong</h4>
-        <p class="mb-0"><code>{{ message }}</code></p>
+        <p class="mb-0"><code>{{ message | replace('\n', '<br>') | safe }}</code></p>
       </div>
       <a href="{{ url_for('index') }}" class="btn btn-outline-secondary btn-sm">Back to home</a>
     </div>