feat(website): 官网企业版视觉升级

- 引入 Geist 字体，去除紫色渐变，克制阴影与交互态
- 导航/卡片/按钮统一企业风格，各区块视觉收敛

website/src/components/SectionShell.tsx

@@ -25,12 +25,12 @@ export default function SectionShell({ id, title, subtitle, children }: SectionS
         <div className="mb-12 max-w-3xl">
           <h2
             id={`${id}-title`}
-            className="text-3xl font-bold tracking-tight md:text-4xl"
+            className="text-3xl font-bold tracking-[-0.03em] md:text-4xl"
           >
             {title}
           </h2>
           {subtitle && (
-            <p className="mt-3 text-base text-muted-foreground">{subtitle}</p>
+            <p className="mt-3 text-base leading-relaxed text-muted-foreground">{subtitle}</p>
           )}
         </div>
         {children}