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/server/middleware/auth_subject.go

@@ -1,28 +1,28 @@
-package middleware
-
-import "github.com/gin-gonic/gin"
-
-// AuthSubject is the minimal authenticated identity stored in gin context.
-// Decision: {UserID int64, Concurrency int}
-type AuthSubject struct {
-	UserID      int64
-	Concurrency int
-}
-
-func GetAuthSubjectFromContext(c *gin.Context) (AuthSubject, bool) {
-	value, exists := c.Get(string(ContextKeyUser))
-	if !exists {
-		return AuthSubject{}, false
-	}
-	subject, ok := value.(AuthSubject)
-	return subject, ok
-}
-
-func GetUserRoleFromContext(c *gin.Context) (string, bool) {
-	value, exists := c.Get(string(ContextKeyUserRole))
-	if !exists {
-		return "", false
-	}
-	role, ok := value.(string)
-	return role, ok
-}
+package middleware
+
+import "github.com/gin-gonic/gin"
+
+// AuthSubject is the minimal authenticated identity stored in gin context.
+// Decision: {UserID int64, Concurrency int}
+type AuthSubject struct {
+	UserID      int64
+	Concurrency int
+}
+
+func GetAuthSubjectFromContext(c *gin.Context) (AuthSubject, bool) {
+	value, exists := c.Get(string(ContextKeyUser))
+	if !exists {
+		return AuthSubject{}, false
+	}
+	subject, ok := value.(AuthSubject)
+	return subject, ok
+}
+
+func GetUserRoleFromContext(c *gin.Context) (string, bool) {
+	value, exists := c.Get(string(ContextKeyUserRole))
+	if !exists {
+		return "", false
+	}
+	role, ok := value.(string)
+	return role, ok
+}