refactor(Dashboard): 调整仪表盘标签文字大小为18px

本次调整仅修改了Dashboard组件中MetricCard的标签文字字号，将原本13px的标签文字调整为18px，统一仪表盘区域的文字视觉层级，让页面信息展示更清晰。

src/Dashboard/index.tsx

@@ -28,7 +28,7 @@ function MetricCard({ label, value, icon }: MetricCardProps & { icon: string })
         <div className="flex h-11 w-11 items-center justify-center rounded-xl bg-white/80 shadow-sm ring-1 ring-black/[0.03]">
           {METRIC_ICONS[icon]}
         </div>
-        <span className="text-[13px] font-medium text-muted">{label}</span>
+        <span className="text-[18px] font-medium text-muted">{label}</span>
       </div>
       <div className="text-[30px] font-bold tracking-tight text-ink">{value}</div>
     </div>