Show 'Job not found' error for invalid jobids

## Show 'Job not found' error for invalid jobids
### Summary
Requesting job details for an invalid job id does not show an error. Instead it shows a blank page. We should show 'Job not found' similarly to the dataset details for invalid pids.

### Steps to Reproduce
Visit `/user/jobs/invalid_job_id`

### Current Behaviour
Here's what I see for `/user/jobs/invalid_job_id` on the frontend using the v4 backend:

<img width="650" height="411" alt="Image" src="https://github.com/user-attachments/assets/b4ea3b06-6aeb-4bc3-a456-efe87fa8981e" />

### Expected Behaviour
It should instead look like the dataset error page:

<img width="1033" height="281" alt="Image" src="https://github.com/user-attachments/assets/7653fb7e-c05b-44de-bfce-964389173b71" />


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Show 'Job not found' error for invalid jobids #1974