feat(Jwt): 重构 JWT 组件，新增常量和结果视图

- 新增 constants.ts 文件，定义 JWT 输入占位符和配置常量，提升代码可读性。
- 删除 JwtSection 组件，重构为 JwtResultView 组件，简化结果展示逻辑。
- 更新 index.tsx，使用 JwtResultView 组件替代原有的 JWT 结果展示方式，优化页面结构。

src/pages/Jwt/constants.ts

@@ -0,0 +1,41 @@
+export const JWT_INPUT_PLACEHOLDER = '在此粘贴 JWT 令牌 (Encoded JWT)...';
+
+export type JwtSectionContentKey = 'header' | 'payload';
+
+export interface JwtSectionConfig {
+  contentKey: JwtSectionContentKey;
+  title: string;
+  colorClass: string;
+  borderClass: string;
+  bgClass: string;
+}
+
+export const JWT_SECTION_CONFIG: JwtSectionConfig[] = [
+  {
+    contentKey: 'header',
+    title: 'HEADER: 算法 & 令牌类型',
+    colorClass: 'text-[#fb015b] dark:text-rose-400',
+    borderClass: 'border-[#fb015b]/20 dark:border-rose-500/20',
+    bgClass: 'bg-[#fb015b]/5 dark:bg-rose-500/5',
+  },
+  {
+    contentKey: 'payload',
+    title: 'PAYLOAD: 数据',
+    colorClass: 'text-[#a03aff] dark:text-purple-400',
+    borderClass: 'border-[#a03aff]/20 dark:border-purple-500/20',
+    bgClass: 'bg-[#a03aff]/5 dark:bg-purple-500/5',
+  },
+];
+
+export const JWT_SIGNATURE_SECTION = {
+  title: '签名',
+  titleClassName: 'text-muted-foreground/90',
+  containerClassName: 'border border-border bg-secondary/40',
+  emptyLabel: '无签名',
+} as const;
+
+export const JWT_JSON_CONTENT_CLASS =
+  'm-0 p-3 bg-muted/30 dark:bg-muted/10 rounded-lg text-xs font-mono overflow-x-auto whitespace-pre-wrap break-all border border-border/50 text-foreground/90 leading-relaxed select-text';
+
+export const JWT_TEXT_CONTENT_CLASS =
+  'block text-xs font-mono break-all text-foreground/80 bg-muted/30 dark:bg-muted/10 p-3 rounded-lg border border-border/50 leading-relaxed select-text';