Return handler and job_runner_name to admins from the job show endpoint

[afgane]

JobSummary documents handler and job_runner_name as "Only
administrator can see this value", but GET /api/jobs/{id} never returns
them — an admin always gets null for both, while external_id and
command_line on the same response are populated.

Cause

Job.to_dict gates the two groups differently:

if system_details or view == "admin_job_list":
    rval["external_id"] = self.job_runner_external_id
    rval["command_line"] = self.command_line
    rval["traceback"] = self.traceback
if view == "admin_job_list":
    rval["handler"] = self.handler
    rval["job_runner_name"] = self.job_runner_name

GET /api/jobs/{id} goes through view_show_job, which calls
to_dict("element", system_details=is_admin). That reaches the first
branch but never the second, so the two fields are simply absent from the
dict. Because the pydantic models declare them Optional[str] = None,
they serialize as null rather than being omitted, which makes it look
like the values are missing rather than never populated.

Fix

Move handler and job_runner_name into the system_details branch.
The admin_job_list view is unaffected — its condition already includes
system_details, so it keeps returning both.

Why this matters

Anything that reads jobs one at a time loses the runner. The AnVIL tool
test harness records the full job object for every test it runs, so every
report it publishes carries a job_runner_name column that is null on
every row, and which runner a failing job used cannot be recovered after
the instance is gone.

Testing

Adds test_show_system_details_admin_only, asserting both fields are
None for a non-admin and non-None for an admin on the show endpoint.
It uses __history_with_new_dataset, which waits for job completion, so
the values are reliably set by then.

🤖 Generated with Claude Code

[jmchilton]

If the API tests are fine, this looks great to me.

[github-actions]

This PR was merged without a "kind/" label, please correct.