feat(website): 三轮视觉改造与页面过渡动画

改造概要（30项）：
- 第一轮：Hero重构/Section差异化/SocialProof强化/CTA对比度/About架构
- 第二轮：字体优化/背景交替/Solutions差异化/Footer五列/MegaDropdown修复
- 第三轮：卡片交互/表单层级/CTA统一/时间线标记/连接线/三列布局/移动导航/Button微交互/SEO Schema
- P3-2：template.tsx+Framer Motion页面过渡/loading.tsx加载状态
- 清理：删除未用组件/hooks，修复重复移动导航，清理冗余CSS

src/components/ui/back-to-top.tsx

@@ -35,11 +35,11 @@ export function BackToTop() {
           exit={shouldReduceMotion ? {} : { opacity: 0, y: 20, scale: 0.8 }}
           transition={{ duration: 0.2, ease: 'easeOut' }}
           onClick={scrollToTop}
-          className="fixed right-4 bottom-20 md:bottom-8 md:right-8 z-40 p-3 bg-[#C41E3A] text-white rounded-full shadow-lg hover:bg-[#A01830] hover:shadow-xl transition-all duration-200 focus:outline-none focus:ring-2 focus:ring-[#C41E3A] focus:ring-offset-2"
+          className="fixed right-4 bottom-20 md:bottom-8 md:right-8 z-40 p-3 bg-[var(--color-brand-primary)] text-white rounded-full shadow-lg hover:bg-[var(--color-brand-primary-hover)] hover:shadow-xl transition-all duration-200 focus:outline-none focus:ring-2 focus:ring-[var(--color-brand-primary)] focus:ring-offset-2"
           aria-label="返回顶部"
           title="返回顶部"
           style={{
-            boxShadow: '0 4px 14px rgba(196, 30, 58, 0.4)',
+            boxShadow: '0 4px 14px rgba(var(--color-brand-primary-rgb), 0.4)',
           }}
           whileHover={shouldReduceMotion ? {} : { scale: 1.1 }}
           whileTap={shouldReduceMotion ? {} : { scale: 0.95 }}