fix(runner): 修复图像结果转存与任务租约失效

修正非语义字段长 Base64 元数据被误判为媒体的问题，并允许按文件签名识别真实媒体后转存 OSS；同时将网关本地存储失败与上游失败分离，避免重复调用和错误降权。

异步任务复用已分配并发名额前立即刷新租约，租约已丢失时重新排队获取，避免排队耗时侵蚀租约后错误调用上游。生产环境关闭 server-main 尚未实现的进度回调，保留 Gateway 任务详情与事件查询。

验证：API 全量 go test、go vet、gofmt、Kubernetes 渲染、迁移安全检查及真实阿里云 OSS 读写/生命周期验收通过。

apps/api/internal/runner/upload.go

@@ -423,18 +423,16 @@ func generatedRawInlineMediaAsset(key string, value string, siblings map[string]
 	}
 	keyLooksLikeMediaPayload := generatedRawDataMediaPayloadKey(key)
 	contentType := firstNonEmptyString(mediaContentTypeFromItem(siblings), defaultContentTypeForRawMediaKey(key))
-	if !keyLooksLikeMediaPayload && !generatedContentTypeIsMedia(contentType) {
-		return nil, false
-	}
-	if !keyLooksLikeMediaPayload && !strings.HasPrefix(strings.ToLower(raw), "data:") && len(raw) < 128 {
+	if !keyLooksLikeMediaPayload && !generatedContentTypeIsMedia(contentType) && !generatedContentTypeIsDocument(contentType) &&
+		!strings.HasPrefix(strings.ToLower(raw), "data:") && len(raw) < localBinaryGenericBase64MinLength {
 		return nil, false
 	}
 	payload, payloadContentType, ok, err := inlineMediaPayload(raw, keyLooksLikeMediaPayload)
 	if err != nil || !ok || len(payload) == 0 {
 		return nil, false
 	}
-	contentType = firstNonEmptyString(payloadContentType, contentType)
-	if !generatedContentTypeIsMedia(contentType) {
+	contentType = firstNonEmptyString(payloadContentType, contentType, detectGeneratedAssetContentType(payload))
+	if !generatedContentTypeIsMedia(contentType) && !generatedContentTypeIsDocument(contentType) {
 		return nil, false
 	}
 	kind := mediaKindForAsset(taskKind, siblings, key, contentType)