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/pkg/openai/request.go

@@ -1,18 +1,18 @@
-package openai
-
-// CodexCLIUserAgentPrefixes matches Codex CLI User-Agent patterns
-// Examples: "codex_vscode/1.0.0", "codex_cli_rs/0.1.2"
-var CodexCLIUserAgentPrefixes = []string{
-	"codex_vscode/",
-	"codex_cli_rs/",
-}
-
-// IsCodexCLIRequest checks if the User-Agent indicates a Codex CLI request
-func IsCodexCLIRequest(userAgent string) bool {
-	for _, prefix := range CodexCLIUserAgentPrefixes {
-		if len(userAgent) >= len(prefix) && userAgent[:len(prefix)] == prefix {
-			return true
-		}
-	}
-	return false
-}
+package openai
+
+// CodexCLIUserAgentPrefixes matches Codex CLI User-Agent patterns
+// Examples: "codex_vscode/1.0.0", "codex_cli_rs/0.1.2"
+var CodexCLIUserAgentPrefixes = []string{
+	"codex_vscode/",
+	"codex_cli_rs/",
+}
+
+// IsCodexCLIRequest checks if the User-Agent indicates a Codex CLI request
+func IsCodexCLIRequest(userAgent string) bool {
+	for _, prefix := range CodexCLIUserAgentPrefixes {
+		if len(userAgent) >= len(prefix) && userAgent[:len(prefix)] == prefix {
+			return true
+		}
+	}
+	return false
+}