polish(frontend): 修正中文字重发虚，并疏朗首页与数据区

补齐 Noto 600/800 并关闭伪粗；Header 加大加粗导航并加板块入口；去掉灰块底、加大列表行距，站点数据格居中缩小数字。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/PostInteractPanels.tsx

@@ -72,10 +72,10 @@ function QuestionPanel({ postId, state }: { postId: number; state: QuestionState
   };
 
   return (
-    <section className="j13-interact-card">
+    <section className={`j13-interact-card${state.solved ? " is-solved" : " is-unsolved"}`}>
       <div className="flex flex-wrap items-center justify-between gap-3">
         <div>
-          <h2 className="font-semibold text-[15px]" style={{ color: "var(--ink)" }}>
+          <h2 className="text-[15px] font-medium" style={{ color: "var(--ink)" }}>
             问答 · {state.solved ? "已解决" : "未解决"}
           </h2>
           <p className="meta text-[12.5px] mt-1">