feat(accounts): 账号列表显示 Antigravity scope 级别限流状态

- 后端 DTO 新增 scope_rate_limits 字段，从 extra 提取限流信息
- 前端状态列显示 scope 级限流徽章（Claude/Gemini/Image）
- 清除速率限制时同时清除账号级和 scope 级限流（已有实现）

Cherry-picked from slovx2/sub2api: 66f49b67

backend/internal/handler/dto/mappers.go

@@ -204,6 +204,17 @@ func AccountFromServiceShallow(a *service.Account) *Account {
 		}
 	}
 
+	if scopeLimits := a.GetAntigravityScopeRateLimits(); len(scopeLimits) > 0 {
+		out.ScopeRateLimits = make(map[string]ScopeRateLimitInfo, len(scopeLimits))
+		now := time.Now()
+		for scope, remainingSec := range scopeLimits {
+			out.ScopeRateLimits[scope] = ScopeRateLimitInfo{
+				ResetAt:      now.Add(time.Duration(remainingSec) * time.Second),
+				RemainingSec: remainingSec,
+			}
+		}
+	}
+
 	return out
 }