refactor(design-tokens): 全量体系化重建设计令牌

Primitive + Semantic 双层令牌架构,HEX->HSL,明暗双份,@theme inline 暴露为 Tailwind 类。

- 新建 src/app/styles/tokens/ 6 个令牌文件(primitive/semantic-light/semantic-dark/lesson-preparation/tailwind-theme/index)
- globals.css 改为 @import 引入,477->258 行
- 清理 91 处 #hex 硬编码颜色 -> hsl(var(--*))
- 清理 10 处硬编码字体 -> var(--font-family-*)
- 清理 100 文件 Tailwind 任意值(Tier 1 映射/Tier 3 注释豁免)
- 清理 M3 Surface 死代码,升级 --lp-* 令牌(HEX->HSL + 暗色补全)
- 新建 ESLint 自定义规则 no-hardcoded-design-tokens(单词边界正则)
- eslint.config.mjs 新增 no-restricted-syntax 禁止 #hex + 自定义规则加载(pathToFileURL)
- 项目规则新增设计令牌规范强制章节
- 架构图 004/005 同步设计令牌体系节点
- known-issues.md 追加设计令牌问题分类(7 个规则表)

验证: tsc --noEmit 0 errors, npm run lint 0 errors/12 warnings(均为既有问题)

src/app/(dashboard)/student/course-plans/[id]/loading.tsx

@@ -4,11 +4,13 @@ export default function StudentCoursePlanDetailLoading() {
   return (
     <div className="flex h-full flex-col space-y-6 p-8">
       <div className="flex items-center justify-between">
+        {/* arbitrary-value: skeleton placeholder fixed size */}
         <Skeleton className="h-8 w-[240px]" />
       </div>
       <Skeleton className="h-4 w-full max-w-md" />
       <div className="grid gap-4 md:grid-cols-3">
         {Array.from({ length: 3 }).map((_, i) => (
+          // arbitrary-value: skeleton placeholder fixed size
           <Skeleton key={i} className="h-[100px] w-full" />
         ))}
       </div>

src/app/(dashboard)/student/course-plans/loading.tsx

@@ -4,11 +4,14 @@ export default function StudentCoursePlansLoading() {
   return (
     <div className="flex h-full flex-col space-y-8 p-8">
       <div className="space-y-2">
+        {/* arbitrary-value: skeleton placeholder fixed size */}
         <Skeleton className="h-8 w-[180px]" />
+        {/* arbitrary-value: skeleton placeholder fixed size */}
         <Skeleton className="h-4 w-[300px]" />
       </div>
       <div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
         {Array.from({ length: 6 }).map((_, i) => (
+          // arbitrary-value: skeleton placeholder fixed size
           <Skeleton key={i} className="h-[160px] w-full" />
         ))}
       </div>

src/app/(dashboard)/student/lesson-plans/page.tsx

@@ -34,6 +34,7 @@ export default async function StudentLessonPlansPage(): Promise<JSX.Element> {
           fallback={
             <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-4">
               {Array.from({ length: 6 }).map((_, i) => (
+                // arbitrary-value: skeleton placeholder fixed size
                 <Skeleton key={i} className="h-[180px] w-full" />
               ))}
             </div>