end-of-run summary report for a load scenario run

Returns an end-of-run summary report derived from the run's status snapshot — the live snapshot while running, or the retained terminal snapshot once finished. The default JSON form carries counts, latency percentiles, the threshold verdict and per-threshold results. With ?format=junit the same data is rendered as a JUnit-XML <testsuite> (one <testcase> per threshold, a <failure> per breach, plus a "run completed" testcase) so CI consumers render per-threshold pass/fail. 404 if the scenario never ran.