Malformed workflow WebSocket messages are not reported

### Feature Summary

Root cause: `WorkflowWebsocketResource.myOnMsg` parses each message before entering its existing error handler. Malformed JSON therefore escapes without producing the `WorkflowErrorEvent` used for every other request failure.

Before: Malformed JSON throws and the client receives no error event.

Expected: Malformed JSON produces a `WorkflowErrorEvent` and the exception still reaches the WebSocket container.

Reproduction evidence:

1. Check out main at commit `caeb27ea54`.
2. Register a session state and call `myOnMsg` with an incomplete JSON object.
3. Observe that parsing throws before the session receives an error payload.

A focused runtime test failed with 0 tests passing and 1 test failing because the expected send never occurred.

Version and commit evidence:

Main, version 1.3.0 incubating snapshot.

**Commit Hash (Optional)**
`caeb27ea54`

## Browsers

Not applicable. This is a WebSocket server issue.

## Relevant log output

```text
Total number of tests run: 1
Tests: succeeded 0, failed 1, canceled 0, ignored 0, pending 0
```

### Proposed Solution or Design

Expected: Malformed JSON produces a `WorkflowErrorEvent` and the exception still reaches the WebSocket container.

### Affected Area

Workflow Engine (Amber)