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/openai.go

@@ -65,7 +65,7 @@ func (c OpenAIClient) Run(ctx context.Context, request Request) (Response, error
 		}
 	}
 	body["model"] = upstreamModelName(request.Candidate)
-	normalizeOpenAIImageRequestBody(endpointKind, body)
+	normalizeOpenAIImageRequestBody(endpointKind, body, request.OriginalBody)
 	stream := openAIEndpointSupportsStream(endpointKind) && (request.Stream || boolValue(body, "stream"))
 	ensureOpenAIStreamUsage(body, endpointKind, stream)
 	raw, contentType, err := openAIRequestPayload(endpointKind, body, request.Candidate)
@@ -172,10 +172,11 @@ func (c OpenAIClient) Run(ctx context.Context, request Request) (Response, error
 	}, nil
 }
 
-func normalizeOpenAIImageRequestBody(endpointKind string, body map[string]any) {
+func normalizeOpenAIImageRequestBody(endpointKind string, body map[string]any, originalBody map[string]any) {
 	if endpointKind != "images.generations" && endpointKind != "images.edits" {
 		return
 	}
+	normalizeOfficialOpenAIImageSize(body, originalBody)
 	// OpenAI image endpoints express output geometry through size. The Gateway
 	// keeps the generic fields for capability validation and billing, but they
 	// are not valid OpenAI wire parameters.
@@ -185,6 +186,10 @@ func normalizeOpenAIImageRequestBody(endpointKind string, body map[string]any) {
 		"resolution",
 		"width",
 		"height",
+		"platform_id",
+		"platformId",
+		"platform_model_id",
+		"platformModelId",
 	} {
 		delete(body, key)
 	}