feat(antigravity): 从 LoadCodeAssist 复用 TierInfo 提取 plan_type

复用已有 GetTier() 返回的 tier ID（free-tier / g1-pro-tier /
g1-ultra-tier），通过 TierIDToPlanType 映射为 Free / Pro / Ultra，
在 loadProjectIDWithRetry 中顺带提取并写入 credentials.plan_type；
前端增加 Abnormal 异常套餐红色标记。

Made-with: Cursor

backend/internal/service/antigravity_subscription_service.go

@@ -0,0 +1,62 @@
+package service
+
+import (
+	"strings"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
+)
+
+const antigravitySubscriptionAbnormal = "abnormal"
+
+// AntigravitySubscriptionResult 表示订阅检测后的规范化结果。
+type AntigravitySubscriptionResult struct {
+	PlanType           string
+	SubscriptionStatus string
+	SubscriptionError  string
+}
+
+// NormalizeAntigravitySubscription 从 LoadCodeAssistResponse 提取 plan_type + 异常状态。
+// 使用 GetTier()（返回 tier ID）+ TierIDToPlanType 映射。
+func NormalizeAntigravitySubscription(resp *antigravity.LoadCodeAssistResponse) AntigravitySubscriptionResult {
+	if resp == nil {
+		return AntigravitySubscriptionResult{PlanType: "Free"}
+	}
+	if len(resp.IneligibleTiers) > 0 {
+		result := AntigravitySubscriptionResult{
+			PlanType:           "Abnormal",
+			SubscriptionStatus: antigravitySubscriptionAbnormal,
+		}
+		if resp.IneligibleTiers[0] != nil {
+			result.SubscriptionError = strings.TrimSpace(resp.IneligibleTiers[0].ReasonMessage)
+		}
+		return result
+	}
+	tierID := resp.GetTier()
+	return AntigravitySubscriptionResult{
+		PlanType: antigravity.TierIDToPlanType(tierID),
+	}
+}
+
+func applyAntigravitySubscriptionResult(account *Account, result AntigravitySubscriptionResult) (map[string]any, map[string]any) {
+	credentials := make(map[string]any)
+	for k, v := range account.Credentials {
+		credentials[k] = v
+	}
+	credentials["plan_type"] = result.PlanType
+
+	extra := make(map[string]any)
+	for k, v := range account.Extra {
+		extra[k] = v
+	}
+	if result.SubscriptionStatus != "" {
+		extra["subscription_status"] = result.SubscriptionStatus
+	} else {
+		delete(extra, "subscription_status")
+	}
+	if result.SubscriptionError != "" {
+		extra["subscription_error"] = result.SubscriptionError
+	} else {
+		delete(extra, "subscription_error")
+	}
+	return credentials, extra
+}