新增配置管理功能及多存储支持

- 添加管理员端 API，用于获取和更新完整配置。
- 添加公共端 API，用于获取非敏感配置信息。
- 增加本地存储（LocalStorage）、S3（S3Storage）、和 WebDAV（WebDAVStorage）存储类型的实现。
- 支持热更新存储配置和保存配置文件至磁盘。
- 更新 Swagger 文档以包含新接口定义。

internal/storage/s3.go

@@ -0,0 +1,72 @@
+package storage
+
+import (
+	"context"
+	"io"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/config"
+	"github.com/aws/aws-sdk-go-v2/credentials"
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+)
+
+type S3Storage struct {
+	client *s3.Client
+	bucket string
+}
+
+func NewS3Storage(ctx context.Context, endpoint, region, accessKey, secretKey, bucket string, useSSL bool) (*S3Storage, error) {
+	customResolver := aws.EndpointResolverWithOptionsFunc(func(service, region string, options ...interface{}) (aws.Endpoint, error) {
+		if endpoint != "" {
+			return aws.Endpoint{
+				URL:               endpoint,
+				SigningRegion:     region,
+				HostnameImmutable: true,
+			}, nil
+		}
+		return aws.Endpoint{}, &aws.EndpointNotFoundError{}
+	})
+
+	cfg, err := config.LoadDefaultConfig(ctx,
+		config.WithRegion(region),
+		config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(accessKey, secretKey, "")),
+		config.WithEndpointResolverWithOptions(customResolver),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	client := s3.NewFromConfig(cfg)
+	return &S3Storage{
+		client: client,
+		bucket: bucket,
+	}, nil
+}
+
+func (s *S3Storage) Save(ctx context.Context, path string, reader io.Reader) error {
+	_, err := s.client.PutObject(ctx, &s3.PutObjectInput{
+		Bucket: aws.String(s.bucket),
+		Key:    aws.String(path),
+		Body:   reader,
+	})
+	return err
+}
+
+func (s *S3Storage) Open(ctx context.Context, path string) (io.ReadCloser, error) {
+	output, err := s.client.GetObject(ctx, &s3.GetObjectInput{
+		Bucket: aws.String(s.bucket),
+		Key:    aws.String(path),
+	})
+	if err != nil {
+		return nil, err
+	}
+	return output.Body, nil
+}
+
+func (s *S3Storage) Delete(ctx context.Context, path string) error {
+	_, err := s.client.DeleteObject(ctx, &s3.DeleteObjectInput{
+		Bucket: aws.String(s.bucket),
+		Key:    aws.String(path),
+	})
+	return err
+}