fix(test): gofmt 审计日志测试 + 补齐 settings 契约 golden 两新字段

- audit_log_test.go: gofmt map 对齐
- api_contract_test.go: GET /admin/settings 两处 golden 补 session_binding_enabled/audit_log_retention_days

backend/internal/server/api_contract_test.go

@@ -708,6 +708,8 @@ func TestAPIContracts(t *testing.T) {
 						"frontend_url": "",
 						"totp_enabled": false,
 						"totp_encryption_key_configured": false,
+						"session_binding_enabled": true,
+						"audit_log_retention_days": 180,
 						"login_agreement_enabled": false,
 						"login_agreement_mode": "modal",
 						"login_agreement_updated_at": "2026-03-31",
@@ -1020,6 +1022,8 @@ func TestAPIContracts(t *testing.T) {
 						"invitation_code_enabled": false,
 						"totp_enabled": false,
 						"totp_encryption_key_configured": false,
+						"session_binding_enabled": true,
+						"audit_log_retention_days": 180,
 						"login_agreement_enabled": false,
 						"login_agreement_mode": "modal",
 						"login_agreement_updated_at": "2026-03-31",

backend/internal/service/audit_log_test.go

@@ -112,12 +112,12 @@ func TestSessionBindingHash(t *testing.T) {
 
 func TestParseAuditLogRetentionDays(t *testing.T) {
 	cases := map[string]int{
-		"":        defaultAuditLogRetentionDays,
-		"abc":     defaultAuditLogRetentionDays,
-		"90":      90,
-		"0":       0,
-		"-1":      0,
-		"  30  ":  30,
+		"":       defaultAuditLogRetentionDays,
+		"abc":    defaultAuditLogRetentionDays,
+		"90":     90,
+		"0":      0,
+		"-1":     0,
+		"  30  ": 30,
 	}
 	for in, want := range cases {
 		if got := parseAuditLogRetentionDays(in); got != want {