#5498: Cron: honor next-heartbeat

## Summary - stop requesting an immediate heartbeat for main-session jobs when wakeMode is `next-heartbeat` - keep the existing `now` behavior: wait for `runHeartbeatOnce` when available, otherwise fall back to `requestHeartbeatNow` - update the duplicate-timer test to assert no heartbeat poke in the `next-heartbeat` path ## Why `next-heartbeat` is meant to queue work for the next scheduled heartbeat, but the previous implementation still poked the heartbeat immediately (sharing the same fallback path as `now` when `runHeartbeatOnce` wasn’t available). That undermined the intended delay and could contribute to duplicate timer wake-ups when multiple CronService instances are active. ## What changed - split the `wakeMode === "now"` path from `next-heartbeat` in `executeJob` - call `requestHeartbeatNow` only for `now` mode when `runHeartbeatOnce` is unavailable - adjust `CronService prevents duplicate timers` test expectation accordingly ## Compromises / Risks - `next-heartbeat` now strictly waits for the scheduled heartbeat; if a deployment disables or stalls the heartbeat, these jobs will sit queued longer than before ## Testing - Not run (not requested) <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adjusts cron main-session wake behavior so `wakeMode: "next-heartbeat"` no longer pokes the heartbeat immediately, while keeping the existing `"now"` behavior: use `runHeartbeatOnce` when available and fall back to `requestHeartbeatNow` otherwise. It also updates the duplicate-timer regression test accordingly and switches the docs landing page logo markup to Tailwind-based dark/light images. The changes fit into the cron subsystem by refining `executeJob`’s wake-up strategy for main-session jobs in `src/cron/service/timer.ts`, and aligning the test expectations in `src/cron/service.prevents-duplicate-timers.test.ts` to match the intended semantics of `next-heartbeat`. <h3>Confidence Score: 3/5</h3> - This PR is likely safe to merge, but has some behavior/coverage gaps worth double-checking. - The cron logic change is localized and matches the stated intent, but the updated test only verifies that no heartbeat poke happens and doesn’t validate that `next-heartbeat` work is eventually processed. The docs change to root-relative asset paths could also break rendering depending on the hosting/base-path setup. - src/cron/service/timer.ts, src/cron/service.prevents-duplicate-timers.test.ts, docs/index.md <!-- greptile_other_comments_section --> **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->