#17006: fix(heartbeat): skip delivery when showOk is false

Fixes #16974 ## Problem When showOk is set to false, HEARTBEAT_OK responses still leak to the channel instead of being suppressed. ## Solution Skip main heartbeat delivery when visibility.showOk is false, in addition to existing skip logic for HEARTBEAT_TOKEN responses. <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR adds a `shouldSkipDueToShowOk` check to skip heartbeat delivery when `visibility.showOk` is `false`. However, the condition `!visibility.showOk` is too broad — since `showOk` defaults to `false` (in `heartbeat-visibility.ts`), this change will suppress **all** heartbeat deliveries (including substantive alert content) under default configuration when no reasoning payloads are present. - The existing code already correctly suppresses `HEARTBEAT_OK` token delivery via `shouldSkipMain` (based on `normalized.shouldSkip`) and `canAttemptHeartbeatOk` (which checks `visibility.showOk`) - The new `shouldSkipDueToShowOk = !visibility.showOk` unconditionally blocks the main delivery path, even for real content responses that should be delivered - Under default settings, this regression would silently drop all heartbeat alert messages to channels <h3>Confidence Score: 1/5</h3> - This PR introduces a regression that would silently suppress all heartbeat alert delivery under default configuration. - The condition `shouldSkipDueToShowOk = !visibility.showOk` evaluates to `true` under default settings (showOk defaults to false). Combined with `reasoningPayloads.length === 0` (the common case), this causes the early-return skip path to trigger for ALL heartbeat responses — not just HEARTBEAT_OK tokens. The existing code already handles HEARTBEAT_OK suppression correctly via `shouldSkipMain` and `canAttemptHeartbeatOk`. - `src/infra/heartbeat-runner.ts` — the `shouldSkipDueToShowOk` condition on line 610 needs to be scoped more narrowly to avoid suppressing substantive heartbeat content. _{Last reviewed commit: 3a900b2} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->