Only failing runs are now flagged as flaky in cross-run detection

Cross-run flaky detection now flags only the contradicting failure as flaky, not the passing runs from the same commit and scheme. This stops inflated flaky-run counts and flakiness rates, so auto-quarantine thresholds no longer trip from a single flaky commit that was retried many times. The Flaky Runs tab, single run view, and PR comment views still show the full pass/fail breakdown for each flaky group.