fix(scheduler): manual Run-now returns run_ids + fail-fast on offline targets

[finedesignz]

Summary

The Run now button on the Schedules page silently did nothing when:

• the bound session/supervisor was offline (run was grace-queued for up to 10 minutes with no UI signal),
• and even on success, the API returned { ok, status } with no run_ids, while the web layer was typed against { run_ids: string[] }, so it had no run id to track progress with.

Root cause

POST /api/scheduled-tasks/:id/run-now was fire-and-forget. It returned 202 immediately and called dispatcher.runNow(...) in the background. runNow returned void, and offline targets were registered for grace replay (which is correct for cron fires but wrong for manual clicks — the user expects immediate feedback).

Fix

• dispatcher.runNow now returns { runIds: string[] }. All early-return paths push their run id before returning. Backward-compatible — existing call sites (catchup, grace, chain) ignore the return value and still work.
• New isManual opt:
  • resolveTargets empty → error='target_offline' (was 'no_targets') and a scheduled_run_finished WS event fires so the Runs drawer shows the failure immediately.
  • resolved-but-offline target → fail-fast with 'target_offline' instead of grace-queuing.
• /api/scheduled-tasks/:id/run-now now awaits the dispatcher and returns { ok, status, run_ids }.
• SchedulesPage.handleRunNow logs when zero rows are returned (defensive).

hub/src/scheduler/catchup.ts is intentionally untouched (separate owner per branch coordination).

Verification

• bun test hub/test/scheduler.test.ts — 52 pass, 0 fail.
• bun build of both edited hub modules succeeds.
• bunx tsc --noEmit on web/ clean.

Test plan

• Click Run now on a task whose session is online → 202 + run_ids: [<id>]; new row appears in the Runs drawer with status transitioning pending → running → succeeded.
• Click Run now on a task whose target is offline → 202 + run_ids: [<id>]; row appears with status failed, error target_offline (no 10-minute grace silence).
• Click Run now when daily cost cap reached → row appears with status skipped, error daily_cost_cap (existing behavior, now also returns the run id).

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