fix(media): 规范比例与 OpenAI 图像尺寸参数

统一过滤非 x:x 比例，避免默认值参与候选匹配或透传上游。

支持 xK 分辨率归一化，并按 Gemini、Volces 和 OpenAI 的参数规范生成上游请求；OpenAI 显式 WxH 始终保留用户原始尺寸。

验证：在独立临时 worktree 中执行 apps/api 全量 go test ./... -count=1 通过，真实 OpenAI 请求已到达上游但受本地无效凭据阻断。

apps/api/internal/clients/volces.go

@@ -357,16 +357,33 @@ func volcesImageBody(request Request) map[string]any {
 			body["seed"] = -1
 		}
 	}
-	if resolution := strings.TrimSpace(stringFromAny(body["resolution"])); resolution != "" {
+	resolution := normalizedProviderImageResolution(body["resolution"])
+	size := widthHeightSize(body)
+	if volcesImageUsesResolutionSize(request) && resolution != "" {
+		body["size"] = resolution
+	} else if size != "" {
+		body["size"] = size
+	} else if resolution != "" {
 		body["size"] = resolution
 	}
-	if size := widthHeightSize(body); size != "" {
-		body["size"] = size
+	for _, key := range []string{"aspect_ratio", "aspectRatio", "ratio", "resolution", "width", "height"} {
+		delete(body, key)
 	}
 	normalizeVolcesSequentialImageGeneration(body, request)
 	return body
 }
 
+func volcesImageUsesResolutionSize(request Request) bool {
+	modelType := firstNonEmpty(request.ModelType, request.Candidate.ModelType)
+	if capability, ok := request.Candidate.Capabilities[modelType].(map[string]any); ok {
+		if strings.EqualFold(strings.TrimSpace(stringFromAny(capability["size_param_format"])), "resolution") {
+			return true
+		}
+	}
+	model := strings.ToLower(strings.TrimSpace(upstreamModelName(request.Candidate)))
+	return strings.HasPrefix(model, "doubao-seedream-5-0")
+}
+
 func volcesVideoBody(request Request) map[string]any {
 	body := cleanProviderBody(request.Body)
 	body["model"] = upstreamModelName(request.Candidate)
@@ -397,6 +414,10 @@ func cleanProviderBody(body map[string]any) map[string]any {
 		"_gateway_target_protocol",
 		"_compat_provider",
 		"_kling_compat_version",
+		"platform_id",
+		"platformId",
+		"platform_model_id",
+		"platformModelId",
 	} {
 		delete(out, key)
 	}