fix: resolve TypeError in login error display

Added missing span element to login-error div to ensure compatibility with auth.js.

static/index.html

@@ -34,7 +34,10 @@
                 </div>
                 <button type="submit" class="btn btn-primary btn-block">Sign In</button>
             </form>
-            <div id="login-error" class="error-message" style="display: none;"></div>
+            <div id="login-error" class="error-message" style="display: none;">
+                <i class="fas fa-exclamation-circle"></i>
+                <span></span>
+            </div>
         </div>
     </div>