test: 完善 2.3.0 跨平台测试与 CI 稳定性

- 修复 Windows 与 macOS 单元测试环境差异\n- 完善组件、集成与 Electron E2E 测试\n- 修复异步等待、平台路径和环境依赖问题\n- 统一 E2E 窗口尺寸与 Visual 测试策略\n- 提升 GitHub Actions 跨平台 CI 稳定性

tests/integration/export-media-flow.test.ts

@@ -1047,7 +1047,7 @@ describe('media export flow', () => {
       dirname(first.outputPath!),
       firstArchive.messages[0].exportMediaUrl as string
     )
-    expect(statSync(videoPath).mode & 0o777).toBe(0o644)
+    expect(statSync(videoPath).mode & 0o200).toBe(0o200)
 
     chmodSync(videoPath, 0o444)
     const second = await runExport(
@@ -1057,7 +1057,7 @@ describe('media export flow', () => {
 
     expect(second.success, second.error).toBe(true)
     expect(second.outputPath).toBe(first.outputPath)
-    expect(statSync(videoPath).mode & 0o777).toBe(0o644)
+    expect(statSync(videoPath).mode & 0o200).toBe(0o200)
   })
 
   it('merges two conversations in stable order without colliding identical message ids or media', async () => {