docs: add package and exported symbol comments for revive lint compliance

internal/storage/errs.go

@@ -14,14 +14,17 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+// Package storage 提供文件存储抽象层，包括 S3 兼容存储和本地缓存。
 package storage
 
+// ErrS3InitializationFailed S3 存储初始化失败错误
 type ErrS3InitializationFailed struct{}
 
 func (e ErrS3InitializationFailed) Error() string {
 	return errS3InitializationFailed
 }
 
+// LocalCacheError 本地缓存错误
 type LocalCacheError struct{}
 
 func (e LocalCacheError) Error() string {

internal/storage/s3.go

@@ -75,10 +75,12 @@ func init() {
 	log.Printf("[Storage] S3 storage initialized (bucket: %s, prefix: %s, cdn: %s)\n", bucket, keyPrefix, cdnURL)
 }
 
+// IsEnabledFunc 检查 S3 存储是否已初始化（可替换用于测试）
 var IsEnabledFunc = func() bool {
 	return client != nil
 }
 
+// IsEnabled 检查 S3 存储是否可用
 func IsEnabled() bool {
 	return IsEnabledFunc()
 }