fix(github): scope PR reviewer wakes by task key (BLO-7457)

[kkroo]

Summary

• add a stable pr_review:<repo>:<number> task key to GitHub reviewer wakes
• preserve that task key in both wake payload and heartbeat contextSnapshot so reviewer wakes no longer share the null task scope
• add a BLO-7457 regression covering a thin active automation run plus a new reviewer PR wake
• let webhook route tests inject heartbeat test options so they do not dispatch background runs or hit ccrotate during assertions

Verification

• pnpm exec vitest run server/src/__tests__/github-webhook.test.ts
• pnpm --filter @paperclipai/server typecheck

Refs BLO-7457.

[kkroo]

@ally please review BLO-7457. Focus area: GitHub reviewer wakes now carry a stable pr_review:<repo>:<number> taskKey through payload/contextSnapshot, and the regression verifies a rich reviewer wake is not coalesced into a thin null-scope automation run.