fix(frontend): pin the check-in badge typography to the reference values

The badge inherited AKSRT's modern system font stack (--font-body) and the
html reset's antialiased/optimizeLegibility rendering, while the reference
theme renders its body in bootstrap's "Helvetica Neue", Helvetica, Arial,
sans-serif with browser defaults. Same 14px size but a different typeface
and smoothing, so the badge text still read as off-theme after the gradient
fix.

Pin font-family, -webkit-font-smoothing and text-rendering to the reference
body values on the existing scoped badge rule (alongside the line-height
pin) and extend the contract test.

assets/css/main.css

@@ -9655,11 +9655,16 @@ img.alignleft {
     padding: 15px;
 }
 
-/* AKSRT 适配：站点行高（--leading-normal: 1.6）与参考主题 bootstrap
- * 的 1.42857143 不同，用户卡片内的 img-badge（签到书签）钉住参考行高；
- * 字号已随 --text-base 对齐参考主题（14px），无需单独声明。 */
+/* AKSRT 适配：签到书签排版逐字对齐参考主题 bootstrap 的 body 计算值——
+ * 行高 1.42857143（站点 --leading-normal 为 1.6）、字体族
+ * "Helvetica Neue", Helvetica, Arial, sans-serif（站点 --font-body 为
+ * 现代系统栈），并还原浏览器默认的字体平滑与渲染（站点 html 重置为
+ * antialiased + optimizeLegibility）；字号随 --text-base 已是参考的 14px。 */
 .user-card .card-content .img-badge {
     line-height: 1.42857143;
+    font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
+    -webkit-font-smoothing: auto;
+    text-rendering: auto;
 }
 
 .user-card name .display-name {