fix(server): transaction error (#14518)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Events can be dispatched in a detached context to avoid inheriting the
current transaction.

* **Bug Fixes**
* Improved resilience and error handling for event processing (graceful
handling of deleted workspaces and ignorable DB errors).
  * More reliable owner assignment flow when changing document owners.

* **Tests**
  * Added tests for doc content staleness with deleted workspaces.
  * Added permission event tests for missing workspace/editor scenarios.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/__tests__/mocks/eventbus.mock.ts

@@ -8,6 +8,7 @@ export class MockEventBus {
 
   emit = this.stub.emitAsync;
   emitAsync = this.stub.emitAsync;
+  emitDetached = this.stub.emitAsync;
   broadcast = this.stub.broadcast;
 
   last<Event extends EventName>(