统一图片抠图到BGFilter模式

为标准纯色背景请求显式传递background_mode=flat。

将手动去背景迁移到background_mode=complex、seg_model=birefnet、cross_check=off。

删除独立BiRefNet服务地址与超时配置并保留token兼容别名。

同步更新前端provider、定向测试、架构文档与项目决策记录。

src/components/image-editor/useImageCanvasGenerationWorkflow.test.tsx

@@ -1785,7 +1785,7 @@ describe('useImageCanvasGenerationWorkflow', () => {
       height: 768,
       taskId: 'background-removal-task',
       elapsedMs: 1234,
-      provider: 'BiRefNet',
+      provider: 'BgFilter',
     });
     render(
       <GenerationWorkflowHarness
@@ -1874,7 +1874,7 @@ describe('useImageCanvasGenerationWorkflow', () => {
         height: 768,
         taskId: 'background-removal-project-task',
         elapsedMs: 1234,
-        provider: 'BiRefNet',
+        provider: 'BgFilter',
         project: null,
       });
     });
@@ -1929,7 +1929,7 @@ describe('useImageCanvasGenerationWorkflow', () => {
         height: 768,
         taskId: 'background-removal-project-task',
         elapsedMs: 1234,
-        provider: 'BiRefNet',
+        provider: 'BgFilter',
         project: {
           projectId: 'project-1',
           title: '队列项目',

src/components/image-editor/useImageCanvasGenerationWorkflow.ts

@@ -1635,7 +1635,7 @@ export function useImageCanvasGenerationWorkflow({
           originalWidth: result.width,
           originalHeight: result.height,
           sourceType: result.sourceType ?? 'generated',
-          provider: result.provider ?? 'BiRefNet',
+          provider: result.provider ?? 'BgFilter',
           taskId: result.taskId ?? null,
           objectKey: result.resource?.objectKey ?? result.objectKey ?? null,
           assetObjectId:

src/services/image-editor/editorProjectClient.test.ts

@@ -1539,7 +1539,7 @@ describe('editorProjectClient', () => {
       assetObjectId: 'asset-object-cutout',
       taskId: 'background-removal-1',
       elapsedMs: 1200,
-      provider: 'BiRefNet',
+      provider: 'BgFilter',
       project: null,
     });