refactor(P3): Redis 缓存键版本化 — Client 增加 Key() 方法，默认前缀 v1:

backend/internal/video/video_service.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
-	"fmt"
 	"strconv"
 	"strings"
 	"time"
@@ -83,7 +82,7 @@ func (vs *VideoService) Delete(ctx context.Context, id uint, authorID uint) erro
 		return err
 	}
 	if vs.cache != nil {
-		cacheKey := fmt.Sprintf("video:detail:id=%d", id)
+		cacheKey := vs.cache.Key("video:detail:id=%d", id)
 		_ = vs.cache.Del(context.Background(), cacheKey)
 	}
 	return nil
@@ -98,7 +97,7 @@ func (vs *VideoService) ListByAuthorID(ctx context.Context, authorID uint) ([]Vi
 }
 
 func (vs *VideoService) GetDetail(ctx context.Context, id uint) (*Video, error) {
-	cacheKey := fmt.Sprintf("video:detail:id=%d", id)
+	cacheKey := vs.cache.Key("video:detail:id=%d", id)
 
 	getCached := func() (*Video, bool) {
 		opCtx, cancel := context.WithTimeout(ctx, 50*time.Millisecond)
@@ -204,11 +203,11 @@ func (vs *VideoService) UpdatePopularity(ctx context.Context, id uint, change in
 
 	if vs.cache != nil {
 		// 1) 详情缓存：直接失效（最简单靠谱）
-		_ = vs.cache.Del(context.Background(), fmt.Sprintf("video:detail:id=%d", id))
+		_ = vs.cache.Del(context.Background(), vs.cache.Key("video:detail:id=%d", id))
 
 		// 2) 热榜：写到“时间窗ZSET”，不要用 detail key
 		now := time.Now().UTC().Truncate(time.Minute)
-		windowKey := "hot:video:1m:" + now.Format("200601021504")
+		windowKey := vs.cache.Key("hot:video:1m:%s", now.Format("200601021504"))
 		member := strconv.FormatUint(uint64(id), 10)
 
 		opCtx, cancel := context.WithTimeout(ctx, 50*time.Millisecond)