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/settings_view.go

@@ -1,42 +1,42 @@
-package service
-
-type SystemSettings struct {
-	RegistrationEnabled bool
-	EmailVerifyEnabled  bool
-
-	SmtpHost     string
-	SmtpPort     int
-	SmtpUsername string
-	SmtpPassword string
-	SmtpFrom     string
-	SmtpFromName string
-	SmtpUseTLS   bool
-
-	TurnstileEnabled   bool
-	TurnstileSiteKey   string
-	TurnstileSecretKey string
-
-	SiteName     string
-	SiteLogo     string
-	SiteSubtitle string
-	ApiBaseUrl   string
-	ContactInfo  string
-	DocUrl       string
-
-	DefaultConcurrency int
-	DefaultBalance     float64
-}
-
-type PublicSettings struct {
-	RegistrationEnabled bool
-	EmailVerifyEnabled  bool
-	TurnstileEnabled    bool
-	TurnstileSiteKey    string
-	SiteName            string
-	SiteLogo            string
-	SiteSubtitle        string
-	ApiBaseUrl          string
-	ContactInfo         string
-	DocUrl              string
-	Version             string
-}
+package service
+
+type SystemSettings struct {
+	RegistrationEnabled bool
+	EmailVerifyEnabled  bool
+
+	SmtpHost     string
+	SmtpPort     int
+	SmtpUsername string
+	SmtpPassword string
+	SmtpFrom     string
+	SmtpFromName string
+	SmtpUseTLS   bool
+
+	TurnstileEnabled   bool
+	TurnstileSiteKey   string
+	TurnstileSecretKey string
+
+	SiteName     string
+	SiteLogo     string
+	SiteSubtitle string
+	ApiBaseUrl   string
+	ContactInfo  string
+	DocUrl       string
+
+	DefaultConcurrency int
+	DefaultBalance     float64
+}
+
+type PublicSettings struct {
+	RegistrationEnabled bool
+	EmailVerifyEnabled  bool
+	TurnstileEnabled    bool
+	TurnstileSiteKey    string
+	SiteName            string
+	SiteLogo            string
+	SiteSubtitle        string
+	ApiBaseUrl          string
+	ContactInfo         string
+	DocUrl              string
+	Version             string
+}