feat: 数据库定时备份与恢复（S3 兼容存储，支持 Cloudflare R2）

新增管理员专属的数据库备份与恢复功能：
- 全量 PostgreSQL 备份（pg_dump），gzip 压缩后上传到 S3 兼容存储
- 支持手动备份和 cron 定时备份
- 支持从备份恢复（psql --single-transaction）
- 备份文件自动过期清理（默认 14 天）
- 前端完整管理页面（S3 配置、定时配置、备份列表、恢复/下载/删除）
- 内置 Cloudflare R2 配置教程弹窗
- Dockerfile 从 postgres 镜像多阶段复制 pg_dump/psql，确保版本一致

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/handler/admin/backup_handler.go

@@ -0,0 +1,170 @@
+package admin
+
+import (
+	"github.com/Wei-Shaw/sub2api/internal/pkg/response"
+	"github.com/Wei-Shaw/sub2api/internal/service"
+	"github.com/gin-gonic/gin"
+)
+
+type BackupHandler struct {
+	backupService *service.BackupService
+}
+
+func NewBackupHandler(backupService *service.BackupService) *BackupHandler {
+	return &BackupHandler{backupService: backupService}
+}
+
+// ─── S3 配置 ───
+
+func (h *BackupHandler) GetS3Config(c *gin.Context) {
+	cfg, err := h.backupService.GetS3Config(c.Request.Context())
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, cfg)
+}
+
+func (h *BackupHandler) UpdateS3Config(c *gin.Context) {
+	var req service.BackupS3Config
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "Invalid request: "+err.Error())
+		return
+	}
+	cfg, err := h.backupService.UpdateS3Config(c.Request.Context(), req)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, cfg)
+}
+
+func (h *BackupHandler) TestS3Connection(c *gin.Context) {
+	var req service.BackupS3Config
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "Invalid request: "+err.Error())
+		return
+	}
+	err := h.backupService.TestS3Connection(c.Request.Context(), req)
+	if err != nil {
+		response.Success(c, gin.H{"ok": false, "message": err.Error()})
+		return
+	}
+	response.Success(c, gin.H{"ok": true, "message": "connection successful"})
+}
+
+// ─── 定时备份 ───
+
+func (h *BackupHandler) GetSchedule(c *gin.Context) {
+	cfg, err := h.backupService.GetSchedule(c.Request.Context())
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, cfg)
+}
+
+func (h *BackupHandler) UpdateSchedule(c *gin.Context) {
+	var req service.BackupScheduleConfig
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "Invalid request: "+err.Error())
+		return
+	}
+	cfg, err := h.backupService.UpdateSchedule(c.Request.Context(), req)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, cfg)
+}
+
+// ─── 备份操作 ───
+
+type CreateBackupRequest struct {
+	ExpireDays *int `json:"expire_days"` // nil=使用默认值14，0=永不过期
+}
+
+func (h *BackupHandler) CreateBackup(c *gin.Context) {
+	var req CreateBackupRequest
+	_ = c.ShouldBindJSON(&req) // 允许空 body
+
+	expireDays := 14 // 默认14天过期
+	if req.ExpireDays != nil {
+		expireDays = *req.ExpireDays
+	}
+
+	record, err := h.backupService.CreateBackup(c.Request.Context(), "manual", expireDays)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, record)
+}
+
+func (h *BackupHandler) ListBackups(c *gin.Context) {
+	records, err := h.backupService.ListBackups(c.Request.Context())
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	if records == nil {
+		records = []service.BackupRecord{}
+	}
+	response.Success(c, gin.H{"items": records})
+}
+
+func (h *BackupHandler) GetBackup(c *gin.Context) {
+	backupID := c.Param("id")
+	if backupID == "" {
+		response.BadRequest(c, "backup ID is required")
+		return
+	}
+	record, err := h.backupService.GetBackupRecord(c.Request.Context(), backupID)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, record)
+}
+
+func (h *BackupHandler) DeleteBackup(c *gin.Context) {
+	backupID := c.Param("id")
+	if backupID == "" {
+		response.BadRequest(c, "backup ID is required")
+		return
+	}
+	if err := h.backupService.DeleteBackup(c.Request.Context(), backupID); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, gin.H{"deleted": true})
+}
+
+func (h *BackupHandler) GetDownloadURL(c *gin.Context) {
+	backupID := c.Param("id")
+	if backupID == "" {
+		response.BadRequest(c, "backup ID is required")
+		return
+	}
+	url, err := h.backupService.GetBackupDownloadURL(c.Request.Context(), backupID)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, gin.H{"url": url})
+}
+
+// ─── 恢复操作 ───
+
+func (h *BackupHandler) RestoreBackup(c *gin.Context) {
+	backupID := c.Param("id")
+	if backupID == "" {
+		response.BadRequest(c, "backup ID is required")
+		return
+	}
+	if err := h.backupService.RestoreBackup(c.Request.Context(), backupID); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+	response.Success(c, gin.H{"restored": true})
+}