fix(ui): 全站视觉审查修复 — 深色模式适配与交互优化

- 法律页面(条款/隐私) Hero 渐变背景深色模式适配，新增 --color-hero-dark-end 变量
- Badge secondary 变体深色模式下从白底白字改为主题自适应灰底
- 首页 Hero 快速导航图标 strokeWidth 加粗提升可读性 (1.8→2.2)
- 服务详情挑战卡片添加 border + hover 边框变色增强层次感
- 移动端 Tab Bar 激活指示器升级为顶部+底部双信号

src/app/(marketing)/services/[id]/client.tsx

@@ -101,7 +101,7 @@ export function ServiceDetailClient({ service }: ServiceDetailClientProps) {
               {serviceChallenges.map((challenge, index) => (
                 <div
                   key={index}
-                  className="p-4 bg-[var(--color-bg-tertiary)] rounded-lg hover:bg-[var(--color-brand-primary-bg)] transition-colors"
+                  className="p-4 bg-[var(--color-bg-tertiary)] rounded-lg border border-[var(--color-border-primary)] hover:border-[var(--color-brand-primary)]/30 hover:bg-[var(--color-brand-primary-bg)] transition-colors"
                 >
                   <h3 className="font-semibold text-[var(--color-text-primary)] mb-1 text-sm">{challenge.title}</h3>
                   <p className="text-sm text-[var(--color-text-muted)]">{challenge.description}</p>

src/app/globals.css

@@ -66,6 +66,7 @@
 
   --color-footer-bg: #1C1C1C;
   --color-cta-bg: #FAFAFA;
+  --color-hero-dark-end: #1C1C1C;
   --color-footer-text: #A0A0A0;
   --color-footer-text-muted: #666666;
   --color-footer-text-dim: #999999;
@@ -200,6 +201,7 @@
 
   --color-footer-bg: #000000;
   --color-cta-bg: #141414;
+  --color-hero-dark-end: #1A0A10;
   --color-footer-text: #8C8C8C;
   --color-footer-text-muted: #525252;
   --color-footer-text-dim: #737373;

src/app/privacy/page.tsx

@@ -9,7 +9,7 @@ export const metadata: Metadata = {
 export default function PrivacyPolicyPage() {
   return (
     <div className="min-h-screen bg-[var(--color-bg-primary)]">
-      <div className="bg-gradient-to-br from-[var(--color-brand-primary)] to-[var(--color-text-primary)] py-20">
+      <div className="bg-gradient-to-br from-[var(--color-brand-primary)] via-[var(--color-brand-primary)]/80 to-[var(--color-hero-dark-end)] py-20">
         <div className="container-wide">
           <h1 className="text-4xl md:text-5xl font-bold text-white mb-4">
             隐私政策

src/app/terms/page.tsx

@@ -9,7 +9,7 @@ export const metadata: Metadata = {
 export default function TermsOfServicePage() {
   return (
     <div className="min-h-screen bg-[var(--color-bg-primary)]">
-      <div className="bg-gradient-to-br from-[var(--color-brand-primary)] to-[var(--color-text-primary)] py-20">
+      <div className="bg-gradient-to-br from-[var(--color-brand-primary)] via-[var(--color-brand-primary)]/80 to-[var(--color-hero-dark-end)] py-20">
         <div className="container-wide">
           <h1 className="text-4xl md:text-5xl font-bold text-white mb-4">
             服务条款