Refactor error handling in HTMLLoader, enhance error templates, and add new entry and setup templates

public/templates/error/error.html

@@ -11,6 +11,10 @@
         <div class="icon">
             ⚠️
         </div>
+        <div class="text">
+            <h2>Error</h2>
+            <p>%error%</p>
+        </div>
     </div>
 </body>
 </html>