revert: completely remove all Sora functionality

backend/internal/service/group.go

@@ -26,15 +26,6 @@ type Group struct {
 	ImagePrice2K *float64
 	ImagePrice4K *float64
 
-	// Sora 按次计费配置（阶段 1）
-	SoraImagePrice360          *float64
-	SoraImagePrice540          *float64
-	SoraVideoPricePerRequest   *float64
-	SoraVideoPricePerRequestHD *float64
-
-	// Sora 存储配额
-	SoraStorageQuotaBytes int64
-
 	// Claude Code 客户端限制
 	ClaudeCodeOnly  bool
 	FallbackGroupID *int64
@@ -112,18 +103,6 @@ func (g *Group) GetImagePrice(imageSize string) *float64 {
 	}
 }
 
-// GetSoraImagePrice 根据 Sora 图片尺寸返回价格（360/540）
-func (g *Group) GetSoraImagePrice(imageSize string) *float64 {
-	switch imageSize {
-	case "360":
-		return g.SoraImagePrice360
-	case "540":
-		return g.SoraImagePrice540
-	default:
-		return g.SoraImagePrice360
-	}
-}
-
 // IsGroupContextValid reports whether a group from context has the fields required for routing decisions.
 func IsGroupContextValid(group *Group) bool {
 	if group == nil {