test(features): remove unsafe test assertions

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/team-mode/team-runtime/cleanup-team-run-resources.test.ts

@@ -41,9 +41,9 @@ function createRuntimeState(teamRunId: string): RuntimeState {
 }
 
 function createStubBgMgr(): BackgroundManager {
-  return {
+  return testCoerce<BackgroundManager>({
     cancelTask: async () => undefined,
-  } as unknown as BackgroundManager
+  })
 }
 
 describe("cleanupTeamRunResources", () => {