feat(openai): 同步生图 API 支持并接入图片计费调度

- 同步 OpenAI 图片生成与编辑接口
- 接入图片请求解析、账号调度、转发与用量记录
- 接入图片计费与图片用量落库
- 限制 OAuth 生图仅支持无显式模型和尺寸的基础请求

backend/internal/service/account.go

@@ -911,6 +911,34 @@ func (a *Account) GetChatGPTAccountID() string {
 	return a.GetCredential("chatgpt_account_id")
 }
 
+func (a *Account) GetOpenAIDeviceID() string {
+	if !a.IsOpenAIOAuth() {
+		return ""
+	}
+	return strings.TrimSpace(a.GetExtraString("openai_device_id"))
+}
+
+func (a *Account) GetOpenAISessionID() string {
+	if !a.IsOpenAIOAuth() {
+		return ""
+	}
+	return strings.TrimSpace(a.GetExtraString("openai_session_id"))
+}
+
+func (a *Account) SupportsOpenAIImageCapability(capability OpenAIImagesCapability) bool {
+	if !a.IsOpenAI() {
+		return false
+	}
+	switch capability {
+	case OpenAIImagesCapabilityBasic:
+		return a.Type == AccountTypeOAuth || a.Type == AccountTypeAPIKey
+	case OpenAIImagesCapabilityNative:
+		return a.Type == AccountTypeAPIKey
+	default:
+		return true
+	}
+}
+
 func (a *Account) GetChatGPTUserID() string {
 	if !a.IsOpenAIOAuth() {
 		return ""