Align console behavior with operator routing and image workflow expectations

Constraint: Must preserve current exchange-rate logic, same-group routing boundary, and temporary image-file behavior while fixing UX-visible inconsistencies.
Rejected: Large frontend chunk refactor | introduced risky circular chunking and did not improve deliverability for this rollout.
Confidence: medium
Scope-risk: moderate
Directive: Keep channel failover constrained to the selected group and preserve Beijing-day semantics for user cache dashboard metrics.
Tested: go test ./controller ./model ./service ./common -count=1; npm run build; remote smoke on source deployment at http://38.76.218.56:18081/ plus /api/status and /api/image-studio/settings.
Not-tested: Browser-driven end-to-end verification of every console page interaction.

model/option.go

@@ -162,6 +162,8 @@ func InitOptionMap() {
 	common.OptionMap["SensitiveWords"] = setting.SensitiveWordsToString()
 	common.OptionMap["ImageStudioSafetyPrompt"] = setting.ImageStudioSafetyPromptToString()
 	common.OptionMap["ImageStudioBannedWords"] = setting.ImageStudioBannedWordsToString()
+	common.OptionMap["ImageStudioSettings"] = `{"enabled":true,"default_model":"gpt-image-2","allow_open_original":true,"retention_minutes":30,"allowed_models":[],"model_settings":[]}`
+	common.OptionMap["ImageStudioRetentionMinutes"] = "30"
 	common.OptionMap["StreamCacheQueueLength"] = strconv.Itoa(setting.StreamCacheQueueLength)
 	common.OptionMap["AutomaticDisableKeywords"] = operation_setting.AutomaticDisableKeywordsToString()
 	common.OptionMap["AutomaticDisableStatusCodes"] = operation_setting.AutomaticDisableStatusCodesToString()
@@ -503,6 +505,10 @@ func updateOptionMap(key string, value string) (err error) {
 		setting.ImageStudioSafetyPromptFromString(value)
 	case "ImageStudioBannedWords":
 		setting.ImageStudioBannedWordsFromString(value)
+	case "ImageStudioSettings":
+		// 由控制器/前端按 JSON 读取；这里仅保留在 OptionMap 中供运行时使用。
+	case "ImageStudioRetentionMinutes":
+		// 由图片制作运行时读取 OptionMap 并解析，避免再引入重复全局状态。
 	case "AutomaticDisableKeywords":
 		operation_setting.AutomaticDisableKeywordsFromString(value)
 	case "AutomaticDisableStatusCodes":