feat: 品牌重命名 Sub2API -> TianShuAPI

- 前端: 所有界面显示、i18n 文本、组件中的品牌名称
- 后端: 服务层、设置默认值、邮件模板、安装向导
- 数据库: 迁移脚本注释
- 保持功能完全一致，仅更改品牌名称

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/internal/service/group.go

@@ -1,49 +1,49 @@
-package service
-
-import "time"
-
-type Group struct {
-	ID             int64
-	Name           string
-	Description    string
-	Platform       string
-	RateMultiplier float64
-	IsExclusive    bool
-	Status         string
-
-	SubscriptionType    string
-	DailyLimitUSD       *float64
-	WeeklyLimitUSD      *float64
-	MonthlyLimitUSD     *float64
-	DefaultValidityDays int
-
-	CreatedAt time.Time
-	UpdatedAt time.Time
-
-	AccountGroups []AccountGroup
-	AccountCount  int64
-}
-
-func (g *Group) IsActive() bool {
-	return g.Status == StatusActive
-}
-
-func (g *Group) IsSubscriptionType() bool {
-	return g.SubscriptionType == SubscriptionTypeSubscription
-}
-
-func (g *Group) IsFreeSubscription() bool {
-	return g.IsSubscriptionType() && g.RateMultiplier == 0
-}
-
-func (g *Group) HasDailyLimit() bool {
-	return g.DailyLimitUSD != nil && *g.DailyLimitUSD > 0
-}
-
-func (g *Group) HasWeeklyLimit() bool {
-	return g.WeeklyLimitUSD != nil && *g.WeeklyLimitUSD > 0
-}
-
-func (g *Group) HasMonthlyLimit() bool {
-	return g.MonthlyLimitUSD != nil && *g.MonthlyLimitUSD > 0
-}
+package service
+
+import "time"
+
+type Group struct {
+	ID             int64
+	Name           string
+	Description    string
+	Platform       string
+	RateMultiplier float64
+	IsExclusive    bool
+	Status         string
+
+	SubscriptionType    string
+	DailyLimitUSD       *float64
+	WeeklyLimitUSD      *float64
+	MonthlyLimitUSD     *float64
+	DefaultValidityDays int
+
+	CreatedAt time.Time
+	UpdatedAt time.Time
+
+	AccountGroups []AccountGroup
+	AccountCount  int64
+}
+
+func (g *Group) IsActive() bool {
+	return g.Status == StatusActive
+}
+
+func (g *Group) IsSubscriptionType() bool {
+	return g.SubscriptionType == SubscriptionTypeSubscription
+}
+
+func (g *Group) IsFreeSubscription() bool {
+	return g.IsSubscriptionType() && g.RateMultiplier == 0
+}
+
+func (g *Group) HasDailyLimit() bool {
+	return g.DailyLimitUSD != nil && *g.DailyLimitUSD > 0
+}
+
+func (g *Group) HasWeeklyLimit() bool {
+	return g.WeeklyLimitUSD != nil && *g.WeeklyLimitUSD > 0
+}
+
+func (g *Group) HasMonthlyLimit() bool {
+	return g.MonthlyLimitUSD != nil && *g.MonthlyLimitUSD > 0
+}