Sayay-007: pipe allow/warn/degrade/block decisions into Qhaway as
sayay.check spans, exposed as qhaway_sayay_decisions_total.

- src/qhaway.ts: SayayQhawayPlugin (onDecision handler, zero hard deps,
  QhawayStorage-compatible) + sayayDecisionMetric helper
- examples/sayay-qhaway.ts + examples/README.md (self-reference via exports)
- README: Qhaway observability section
- package.json: version 0.3.0, added exports map (import/require/types)
- tests: 5 new (total 17/17)