feat(skills): add flaky-test-judge

[bbbbzzzzcc-afk]

Summary

• add the flaky-test-judge runx skill for evidence-based quarantine, keep-enabled, fix-now, environmental-noise, human-review, and missing-evidence decisions
• emit a typed runx.flaky.test_triage.v1 handoff without mutating repositories or starting downstream PR workflows
• include exactly two hosted harness cases: a sealed 65% pass-rate quarantine case and a sealed missing-run-history stop case
• include standalone fixtures for both acceptance paths

Operator value

The skill turns supplied test history and release policy into a bounded, auditable disposition. Quarantine output contains a temporary exclusion marker and an issue-to-pr handoff template, while repository mutation remains behind a separate governed run and human merge gate.

Validation

• runx --version → runx-cli 0.6.14
• runx harness ./skills/flaky-test-judge → passed, 2 cases, 0 assertion errors
• cases: quarantine_justified, missing_run_history
• git diff --check