fix(orchestration): keep heartbeats from waking coordinators

[portrah]

Summary

• keep valid orchestration heartbeats out of push-on-idle wake batches
• preserve rejected heartbeats as high-priority coordinator notifications
• leave valid heartbeat rows unread so explicit heartbeat checks remain auditable

Why

Heartbeat-only traffic currently starts coordinator turns and accumulated heartbeats can inflate a later wake batch. Heartbeats already update dispatch liveness during lifecycle reconciliation, so they do not need to wake an idle coordinator.

Verification

• pnpm exec vitest run --config config/vitest.config.ts src/main/runtime/orca-runtime.test.ts (1074 passed, 1 skipped)
• pnpm run typecheck
• pnpm exec oxlint src/main/runtime/orchestration/db.ts src/main/runtime/orca-runtime.ts src/main/runtime/orca-runtime.test.ts

[Jinwoo-H]

Closing this submitted branch and routing the heartbeat wake-suppression bug to canonical issue #14910. Newer owner PR #15173 covers the same wake half together with the required heartbeat-read surface; we will own the final current-main implementation there. Full credit to @portrah is preserved. No action is requested from you. Thank you.