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/usage_log.go

@@ -1,53 +1,53 @@
-package service
-
-import "time"
-
-const (
-	BillingTypeBalance      int8 = 0 // 钱包余额
-	BillingTypeSubscription int8 = 1 // 订阅套餐
-)
-
-type UsageLog struct {
-	ID        int64
-	UserID    int64
-	ApiKeyID  int64
-	AccountID int64
-	RequestID string
-	Model     string
-
-	GroupID        *int64
-	SubscriptionID *int64
-
-	InputTokens         int
-	OutputTokens        int
-	CacheCreationTokens int
-	CacheReadTokens     int
-
-	CacheCreation5mTokens int
-	CacheCreation1hTokens int
-
-	InputCost         float64
-	OutputCost        float64
-	CacheCreationCost float64
-	CacheReadCost     float64
-	TotalCost         float64
-	ActualCost        float64
-	RateMultiplier    float64
-
-	BillingType  int8
-	Stream       bool
-	DurationMs   *int
-	FirstTokenMs *int
-
-	CreatedAt time.Time
-
-	User         *User
-	ApiKey       *ApiKey
-	Account      *Account
-	Group        *Group
-	Subscription *UserSubscription
-}
-
-func (u *UsageLog) TotalTokens() int {
-	return u.InputTokens + u.OutputTokens + u.CacheCreationTokens + u.CacheReadTokens
-}
+package service
+
+import "time"
+
+const (
+	BillingTypeBalance      int8 = 0 // 钱包余额
+	BillingTypeSubscription int8 = 1 // 订阅套餐
+)
+
+type UsageLog struct {
+	ID        int64
+	UserID    int64
+	ApiKeyID  int64
+	AccountID int64
+	RequestID string
+	Model     string
+
+	GroupID        *int64
+	SubscriptionID *int64
+
+	InputTokens         int
+	OutputTokens        int
+	CacheCreationTokens int
+	CacheReadTokens     int
+
+	CacheCreation5mTokens int
+	CacheCreation1hTokens int
+
+	InputCost         float64
+	OutputCost        float64
+	CacheCreationCost float64
+	CacheReadCost     float64
+	TotalCost         float64
+	ActualCost        float64
+	RateMultiplier    float64
+
+	BillingType  int8
+	Stream       bool
+	DurationMs   *int
+	FirstTokenMs *int
+
+	CreatedAt time.Time
+
+	User         *User
+	ApiKey       *ApiKey
+	Account      *Account
+	Group        *Group
+	Subscription *UserSubscription
+}
+
+func (u *UsageLog) TotalTokens() int {
+	return u.InputTokens + u.OutputTokens + u.CacheCreationTokens + u.CacheReadTokens
+}