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/gemini_token_cache.go

@@ -1,16 +1,16 @@
-package service
-
-import (
-	"context"
-	"time"
-)
-
-// GeminiTokenCache stores short-lived access tokens and coordinates refresh to avoid stampedes.
-type GeminiTokenCache interface {
-	// cacheKey should be stable for the token scope; for GeminiCli OAuth we primarily use project_id.
-	GetAccessToken(ctx context.Context, cacheKey string) (string, error)
-	SetAccessToken(ctx context.Context, cacheKey string, token string, ttl time.Duration) error
-
-	AcquireRefreshLock(ctx context.Context, cacheKey string, ttl time.Duration) (bool, error)
-	ReleaseRefreshLock(ctx context.Context, cacheKey string) error
-}
+package service
+
+import (
+	"context"
+	"time"
+)
+
+// GeminiTokenCache stores short-lived access tokens and coordinates refresh to avoid stampedes.
+type GeminiTokenCache interface {
+	// cacheKey should be stable for the token scope; for GeminiCli OAuth we primarily use project_id.
+	GetAccessToken(ctx context.Context, cacheKey string) (string, error)
+	SetAccessToken(ctx context.Context, cacheKey string, token string, ttl time.Duration) error
+
+	AcquireRefreshLock(ctx context.Context, cacheKey string, ttl time.Duration) (bool, error)
+	ReleaseRefreshLock(ctx context.Context, cacheKey string) error
+}