feat: 品牌重命名 Sub2API -> TianShuAPI (基于官方 v0.1.46)

- 基于官方最新代码 upstream/main (93db889)
- 包含所有官方新功能：运维监控、促销码系统、Linux DO OAuth 等
- 仅修改品牌显示名称，保持所有功能完整
- 修改范围：前后端界面文字、i18n、邮件模板、日志输出

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

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

backend/internal/setup/cli.go

@@ -51,7 +51,7 @@ func RunCLI() error {
 
 	fmt.Println()
 	fmt.Println("╔═══════════════════════════════════════════╗")
-	fmt.Println("║       Sub2API Installation Wizard         ║")
+	fmt.Println("║       TianShuAPI Installation Wizard         ║")
 	fmt.Println("╚═══════════════════════════════════════════╝")
 	fmt.Println()