refactor(storage): remove unused helpers and legacy aliases

clear()/hasItem() and the secureStorage/encryptData/decryptData/isEncrypted aliases had no callers. migratePlaintextKeys now reuses isObfuscated instead of duplicating the prefix literal.

src/services/storage/secureStorage.ts

@@ -71,13 +71,6 @@ class ObfuscatedStorageService {
     localStorage.removeItem(key);
   }
 
-  /**
-   * 清空所有数据
-   */
-  clear(): void {
-    localStorage.clear();
-  }
-
   /**
    * 迁移旧的明文缓存为加密格式
    */
@@ -87,7 +80,7 @@ class ObfuscatedStorageService {
       if (!raw) return;
 
       // 如果已经是加密格式，跳过
-      if (raw.startsWith('enc::v1::')) {
+      if (isObfuscated(raw)) {
         return;
       }
 
@@ -106,15 +99,6 @@ class ObfuscatedStorageService {
       }
     });
   }
-
-  /**
-   * 检查键是否存在
-   */
-  hasItem(key: string): boolean {
-    return localStorage.getItem(key) !== null;
-  }
 }
 
 export const obfuscatedStorage = new ObfuscatedStorageService();
-// Backward-compatible alias (historically named "secureStorage").
-export const secureStorage = obfuscatedStorage;

src/utils/encryption.ts

@@ -101,8 +101,3 @@ export function deobfuscateData(payload: string): string {
 export function isObfuscated(value: string): boolean {
   return value?.startsWith(ENC_PREFIX) || false;
 }
-
-// Backward-compatible aliases (this module was historically named "encryption").
-export const encryptData = obfuscateData;
-export const decryptData = deobfuscateData;
-export const isEncrypted = isObfuscated;