feat(9.14.9b): shell-side item alerts — reminders fire with the app closed

[th3-br41n]

Closes the gap 9.14.9 left: due/scheduled task alerts and calendar event reminders ran on a 30s tick inside the app renderer, so nothing fired once the window closed. This hosts the same alerts in the main process on the existing automations SchedulerService — one fire mechanism product-wide, no new scheduling logic.

How it works

• main/automations/item-alerts.ts (pure, +14 tests): Task/v1 + Event/v1 entity rows → one-shot alert registrations, mirroring the app-side semantics (midnight→09:00 task instants, deadline-wins same-instant collision, per-offset event reminders, base-occurrence recurrence fidelity). Dedupe keys replicate the SDK reminderDedupeKey shape.
• AutomationsHost gains an optional postAlert port and routes item-alert fires to it (+4 wiring tests: fire w/ source appId+dedupeKey, event offset fire, live unregister on task completion, exactly-once).
• The deployment derives alerts in hydrateFromEntities, re-derives on any Task/Event write (coalesced, same path as automation-entity writes), reconciles stale ids, and stays host-designation-gated — no multi-device double-fire.
• index.ts posts through the shared UiNotifyHost under the source app's id (io.brainstorm.tasks / io.brainstorm.calendar), so when an app window is open and both schedulers fire, the host's (appId, dedupeKey) window collapses the duplicate. Calendar's in-app notify now passes due.dedupeKey (Tasks already did).

Posture notes

• Alerts missed while the shell was closed do not back-fire (scheduler recomputes from now on vault open — same as Reminder/v1; a catch-up pass is a possible follow-up).
• No new IPC or capability surface: entity reads ride the automations app's existing entities.read:*; postAlert is main-internal; DND/mute/dedupe all enforced by the existing notify host; titles are never persisted (registry stores only ids + fire configs).
• Alert bodies are plain English from main (same as every existing main-posted notification — mentions, tail-truncation warnings); main-process i18n is a product-wide gap, not introduced here.

Verification

• bun run verify green; full suite 14,636 passed (one FTS stress-budget flake under concurrent-run load, passes solo in 17s).
• New e2e (tests/e2e/specs/item-alerts.spec.ts, passes in 1.1m): boot 1 provisions a task with a timed dueAt without ever opening Tasks; boot 2 just reopens the vault — the notification lands in the history attributed to io.brainstorm.tasks within a drain tick. Also proves the alert derives from persisted state across a restart.

Plan: harness docs/implementation-plan.md 9.14.9b ✅ (merged) — 0.1.9 scope row 1 of 2.

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