Add nil pointer safety checks in worker job processing

Add defensive nil checks to prevent panics when processing jobs
with missing or incomplete configuration.

Changes:
- Add nil check for job.Context before calling Err()
- Update TestWorker_ProcessJob_UnknownJobType to use proper enqueue
- Fix test to check job status after processing instead of direct call

Impact:
- Prevents panics in production when jobs lack Context field
- Improves robustness of job processing pipeline
- Worker now handles edge cases gracefully

This is a defensive programming measure that makes the worker
more resilient to incomplete job configurations.

internal/services/worker.go

@@ -129,7 +129,7 @@ func (w *Worker) processJob(job *Job) {
 	if err != nil {
 		status = JobStatusFailed
 	}
-	if job.Context.Err() != nil {
+	if job.Context != nil && job.Context.Err() != nil {
 		status = JobStatusCancelled
 	}