fix: safeStorage 解密失败时回退到 base64 解码

密码可能在 safeStorage 不可用时以纯 base64 存储，或因 keyring 环境
变化导致无法解密。添加 try-catch 回退，避免连接时崩溃。

src/main/credential.ts

@@ -11,5 +11,13 @@ export function decrypt(encoded: string): string {
   if (!safeStorage.isEncryptionAvailable()) {
     return Buffer.from(encoded, 'base64').toString('utf-8')
   }
-  return safeStorage.decryptString(Buffer.from(encoded, 'base64'))
+  try {
+    return safeStorage.decryptString(Buffer.from(encoded, 'base64'))
+  } catch {
+    // Fallback: the ciphertext may have been encoded with plain base64
+    // (e.g. when safeStorage was unavailable at encryption time, or the
+    // OS keyring changed). Decode as plain base64 so the connection
+    // attempt can proceed instead of crashing.
+    return Buffer.from(encoded, 'base64').toString('utf-8')
+  }
 }