refactor: 移除不必要的 export 关键字

中优先级任务：将仅内部使用的函数和类型移除 export 关键字

移除 export 的函数：
- uiPopover: showPopover
- storageCleaner: injectClearLocalStorage, injectClearSessionStorage,
  injectClearIndexedDB, injectClearCacheStorage, injectUnregisterServiceWorkers

移除 export 的类型和常量：
- base64Converter: SUPPORTED_IMAGE_TYPES, SUPPORTED_IMAGE_EXTENSIONS,
  TextToBase64Result, Base64ToBlobResult
- contextMenu: ContextMenuItemConfig, ContextMenuClickedInfo, ParseResult
- jsonFormatter: JsonMinifyResult
- jsonToToml: JsonToTomlResult
- jsonToYaml: JsonToYamlResult
- jwt: JwtHeader, JwtPayload
- qrCodeParser: QrCodeParseResult

所有 473 个测试通过，类型检查通过

src/utils/contextMenu.ts

@@ -1,18 +1,18 @@
 import type { PageType } from '@/types/storage';
 
-export interface ContextMenuItemConfig {
+interface ContextMenuItemConfig {
   id: string;
   title: string;
   contexts: [`${chrome.contextMenus.ContextType}`, ...`${chrome.contextMenus.ContextType}`[]];
   parentId?: string;
 }
 
-export interface ContextMenuClickedInfo {
+interface ContextMenuClickedInfo {
   featureKey: PageType;
   payload: string;
 }
 
-export interface ParseResult {
+interface ParseResult {
   success: boolean;
   data?: ContextMenuClickedInfo;
   error?: string;