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/server/api_contract_test.go

@@ -271,14 +271,14 @@ func TestAPIContracts(t *testing.T) {
 					service.SettingKeySMTPUsername: "user",
 					service.SettingKeySMTPPassword: "secret",
 					service.SettingKeySMTPFrom:     "no-reply@example.com",
-					service.SettingKeySMTPFromName: "Sub2API",
+					service.SettingKeySMTPFromName: "TianShuAPI",
 					service.SettingKeySMTPUseTLS:   "true",
 
 					service.SettingKeyTurnstileEnabled:   "true",
 					service.SettingKeyTurnstileSiteKey:   "site-key",
 					service.SettingKeyTurnstileSecretKey: "secret-key",
 
-					service.SettingKeySiteName:     "Sub2API",
+					service.SettingKeySiteName:     "TianShuAPI",
 					service.SettingKeySiteLogo:     "",
 					service.SettingKeySiteSubtitle: "Subtitle",
 					service.SettingKeyAPIBaseURL:   "https://api.example.com",
@@ -308,7 +308,7 @@ func TestAPIContracts(t *testing.T) {
 					"smtp_username": "user",
 					"smtp_password_configured": true,
 					"smtp_from_email": "no-reply@example.com",
-					"smtp_from_name": "Sub2API",
+					"smtp_from_name": "TianShuAPI",
 					"smtp_use_tls": true,
 					"turnstile_enabled": true,
 					"turnstile_site_key": "site-key",
@@ -321,7 +321,7 @@ func TestAPIContracts(t *testing.T) {
 						"ops_realtime_monitoring_enabled": true,
 						"ops_query_mode_default": "auto",
 						"ops_metrics_interval_seconds": 60,
-						"site_name": "Sub2API",
+						"site_name": "TianShuAPI",
 						"site_logo": "",
 						"site_subtitle": "Subtitle",
 						"api_base_url": "https://api.example.com",