worker exits on malformed task_change payload instead of ignoring

[maxcountryman]

Summary

Malformed JSON payloads on task_change currently propagate an error and can terminate Worker::run_every.

Why this is a problem

The code logs that malformed payloads are being ignored, but returns the deserialization error with ?, which bubbles up and exits the worker loop.

Evidence

• src/worker.rs:691 (serde_json::from_str(payload))
• src/worker.rs:692 logs "Invalid task change payload; ignoring"
• src/worker.rs:694 error is returned via ?

Expected behavior

Malformed notify payloads should be logged and ignored without stopping worker processing.

Proposed direction

• On decode failure, return Ok(()) from handle_task_change after logging.
• Optionally include a metric for malformed notifications.

Acceptance criteria

• Injecting invalid task_change payload does not terminate worker loop.
• Worker continues processing subsequent valid notifications and poll ticks.