refactor(theme): 营销页 bg-white token 化（暗黑模式 Phase 2 · marketing 批次）

问题：Tailwind 原生 bg-white 是硬编码值，深色主题下不翻转，
导致整页/整 section 恒为纯白，与转深色的页头页脚割裂。
（globals.css：--color-bg-primary-rgb 浅色 255 255 255 → 深色 10 14 20）

改动：10 文件 67 处 bg-white → 项目 token，按语义二分类
- bg-bg-primary  （33 处）：页面/大块骨架（min-h-screen 容器、<section>、<main>）
- bg-bg-elevated （34 处）：浮起层（带 border 的卡片、表单输入、图标盒、grid 单元格）
  --color-bg-elevated 浅色 #FFFFFF → 深色 #151B23，同样翻转。

浅色主题下 bg-white / bg-bg-primary / bg-bg-elevated 三者同值（纯白），
故本次改动在浅色主题下零像素差异，只修复深色主题。

新增审计工具：
- scripts/audit/hardcoded-color-audit.mjs：硬编码颜色分级盘点
  （含 alpha 误报修正：bg-white/NN 半透明叠加两主题均成立，判 INFO 非 P0）
- scripts/audit/darkmode-bg-verify.mjs：直接验证背景随主题翻转
  （浅色应纯白、深色应 rgb(10,14,20) 且无残留纯白块）

审计结果：marketing P0 67 → 0；全站 P0 97 → 30
（剩余 components 16 / other 8 / layout 3 / ui-kit 3 为第二批；admin 本就为 0）

门禁：
- tsc 0 error
- eslint 0 error（50 warnings 全为既有，改动文件未新增）
- jest 129/130 套件通过，1548 通过 / 2 跳过 / **0 断言失败**
  唯一失败 src/lib/admin-api.test.ts 为**沙箱环境限制非代码问题**：
  CODEBUDDY_BROKER_DENY 拦截 readFileSync，单独复验同样失败，
  与本次改动零交集（改动仅限 src/app/(marketing)/ 下 10 个页面组件）
- 暗黑模式背景验证 18/18 PASS（9 路由 × 浅深双版）

src/app/(marketing)/solutions/solution-detail-content-v3.tsx

@@ -40,7 +40,7 @@ function DetailHero({ solution }: DetailHeroProps) {
   const industryIcon = INDUSTRY_ICONS[solution.industry] || <Factory className="w-8 h-8" />;
 
   return (
-    <section className="relative min-h-[80vh] flex items-center overflow-hidden bg-white pt-24">
+    <section className="relative min-h-[80vh] flex items-center overflow-hidden bg-bg-primary pt-24">
       <div className="max-w-container mx-auto px-4 sm:px-6 lg:px-10 relative z-10 w-full py-20 sm:py-24 md:py-28 lg:py-32">
         <motion.div
           initial={{ opacity: 0, y: 30 }}
@@ -122,7 +122,7 @@ function ChallengesSection({ challenges }: ChallengesSectionProps) {
               {challenges.map((challenge, idx) => (
                 <div
                   key={idx}
-                  className="group relative p-8 bg-white hover:bg-bg-secondary transition-all duration-150"
+                  className="group relative p-8 bg-bg-elevated hover:bg-bg-secondary transition-all duration-150"
                 >
                   <div className="absolute left-0 top-0 bottom-0 w-1 bg-brand scale-y-0 group-hover:scale-y-100 transition-transform duration-150 origin-top" />
                   <div className="flex items-start gap-6">
@@ -147,7 +147,7 @@ interface SolutionsSectionProps {
 
 function SolutionsSection({ solutions }: SolutionsSectionProps) {
   return (
-    <section className="relative py-20 sm:py-28 md:py-32 lg:py-40 overflow-hidden bg-white">
+    <section className="relative py-20 sm:py-28 md:py-32 lg:py-40 overflow-hidden bg-bg-primary">
       <div className="max-w-container mx-auto px-4 sm:px-6 lg:px-10">
         <ScrollReveal className="text-center max-w-3xl mx-auto mb-16 sm:mb-20 md:mb-20">
           <SectionLabel className="justify-center">
@@ -169,7 +169,7 @@ function SolutionsSection({ solutions }: SolutionsSectionProps) {
             {solutions.map((solution, idx) => (
               <div
                 key={idx}
-                className="group relative p-10 bg-white hover:bg-bg-secondary transition-all duration-150"
+                className="group relative p-10 bg-bg-elevated hover:bg-bg-secondary transition-all duration-150"
               >
                 <div className="absolute top-0 left-0 right-0 h-1 bg-brand scale-x-0 group-hover:scale-x-100 transition-transform duration-150 origin-left" />
 
@@ -226,7 +226,7 @@ function ValuePropositionSection({ valueProposition }: ValuePropositionProps) {
               return (
                 <div
                   key={idx}
-                  className="group relative p-10 text-center bg-white hover:bg-bg-secondary transition-all duration-150"
+                  className="group relative p-10 text-center bg-bg-elevated hover:bg-bg-secondary transition-all duration-150"
                 >
                   <div className="absolute top-0 left-1/2 -translate-x-1/2 w-1/3 h-1 bg-brand scale-x-0 group-hover:scale-x-100 transition-transform duration-150 origin-center" />
 
@@ -257,7 +257,7 @@ function SuiteCombinationSection({ suiteCombination, products }: SuiteCombinatio
     .filter(Boolean);
 
   return (
-    <section className="relative py-20 sm:py-28 md:py-32 lg:py-40 overflow-hidden bg-white">
+    <section className="relative py-20 sm:py-28 md:py-32 lg:py-40 overflow-hidden bg-bg-primary">
       <div className="max-w-container mx-auto px-4 sm:px-6 lg:px-10">
         <ScrollReveal className="text-center max-w-3xl mx-auto mb-16 sm:mb-20 md:mb-20">
           <SectionLabel className="justify-center">
@@ -279,7 +279,7 @@ function SuiteCombinationSection({ suiteCombination, products }: SuiteCombinatio
             {primaryProducts.map((product) => product && (
               <div
                 key={product.id}
-                className="group relative p-8 bg-white hover:bg-bg-secondary transition-all duration-150 text-center lg:col-span-2"
+                className="group relative p-8 bg-bg-elevated hover:bg-bg-secondary transition-all duration-150 text-center lg:col-span-2"
               >
                 <div className="absolute top-0 left-0 right-0 h-1 bg-brand scale-x-0 group-hover:scale-x-100 transition-transform duration-150 origin-left" />
 
@@ -296,7 +296,7 @@ function SuiteCombinationSection({ suiteCombination, products }: SuiteCombinatio
             ))}
           </StaggerReveal>
 
-          <ScrollReveal delay={0.2} className="flex items-center justify-center lg:col-span-1 bg-white">
+          <ScrollReveal delay={0.2} className="flex items-center justify-center lg:col-span-1 bg-bg-elevated">
             <div className="w-20 h-20 rounded-full bg-brand-soft/30 border-2 border-brand/30 flex items-center justify-center text-brand font-bold text-xl">
               +
             </div>