Malformed workflow WebSocket frames are not reported to the editor

### Feature Summary

A malformed workflow WebSocket frame fails during JSON deserialization before the endpoint enters its existing error handler. The server logs the parse exception, but the connected editor receives no `WorkflowErrorEvent` and keeps waiting without an explanation.

Before: malformed frame logs an exception and sends no error event.

After: malformed frame follows the normal workflow error path and sends `WorkflowErrorEvent` with the parse failure.

Valid heartbeat frames must continue to receive `HeartBeatResponse`.

Reproduction evidence:

1. Start the computing unit master from main.
2. Connect to the workflow WebSocket with valid workflow and computing unit parameters.
3. Send the incomplete JSON frame `{`.
4. Observe the normal startup events, but no workflow error event. The client eventually times out.

Version and commit evidence:

1.3.0-incubating-SNAPSHOT main

**Commit Hash**

70c21145887920528d7d5540e3fb790b43e8b759

**What browsers are you seeing the problem on?**

Not browser specific.

**Relevant log output**

`JsonEOFException: Unexpected end-of-input`

### Proposed Solution or Design

After: malformed frame follows the normal workflow error path and sends `WorkflowErrorEvent` with the parse failure.

### Affected Area

Workflow Engine (Amber)