Add systemic thundering herd prevention rules (CC-CONC-009-013)

Implement all ConcurrencyGuard rules

Add ConcurrencyGuard tool and swift-concurrency-guard skill

Add Swift 6.2 hang elimination patterns (Task.immediate, priority escalation, named tasks)

Add async: true to hook for non-blocking analysis

Fix skill name mismatch, add MIT LICENSE

Add all plugin components: 9 skills, 4 commands, 3 agents, 1 hook

Initial plugin structure