feat: 添加媒体播放功能，支持基于短时效token的播放入口及相关API接口

backend/app/http/tenant/dto/content_asset_play.go

@@ -0,0 +1,23 @@
+package dto
+
+import (
+	"encoding/json"
+	"time"
+
+	"quyun/v2/pkg/consts"
+)
+
+// ContentPlayableAsset is a deliverable media asset item with short-lived play URL/token.
+type ContentPlayableAsset struct {
+	AssetID int64                 `json:"asset_id"`
+	Type    consts.MediaAssetType `json:"type"`
+
+	// PlayURL is a short-lived URL; do NOT expose bucket/object_key directly.
+	PlayURL string `json:"play_url"`
+
+	// ExpiresAt indicates when PlayURL/token expires; optional.
+	ExpiresAt *time.Time `json:"expires_at,omitempty"`
+
+	// Meta is a display-safe whitelist (currently passthrough JSON); optional.
+	Meta json.RawMessage `json:"meta,omitempty"`
+}