v3.19.0 — Three catalog plugins + capability-probe retirement

MINOR — three new catalog plugins + developer-workflows 0.24.0: the slug-keyed capability_probe.py is retired in favour of the agentm V5-8 capability resolver (LC-5 downstream), and three new convention/workflow plugins ship their first release.

Added

• testing-conventions 0.1.0 — no-skip-tests rule (any skip/xfail marker requires an exact-technical-blocker comment + issue link) and testing-conventions skill (tests-are-sacred · verification-first · 3-layer pyramid). Reference.
• releasing-conventions 0.1.1 — version-bump-required rule and ship-release skill (pre-release checklist, changelog shape, paired-release discipline, version-bump policy). Reference.
• design-docs 0.1.0 — adr skill (5-section shape with mandatory "why not the alternative" + re-audit triggers) and /design command wrapper (delegates to developer-workflows). Reference.

Changed

• developer-workflows 0.24.0 — capability_probe.py retired; find_capability.py is the live path. All 9 phase-command call-sites migrated to capability-keyed resolver queries (adversarial-review, wiki-maintenance, board-sync). DC-2 preserved: best-effort discovery, graceful-skip when agentm absent.
• code-review 0.2.1 — added capabilities: [adversarial-review] declaration (LC-5 cutover).
• wiki-maintenance 0.2.3 — added capabilities: [wiki-maintenance] declaration (LC-5 cutover).

Internal

• Wiki: three new reference pages; Home.md and sidebar updated.
• ADR 0017 §3 amended: find_capability.py is the live path; re-audit trigger resolved.