feat: test and fix notifications for all cron jobs and reminders #3805

Summary

Notifications are not reliably firing for all cron jobs and reminders. We need to test the full notification surface and ensure every scheduled job, reminder, and trigger correctly surfaces a notification to the user.

Scope

Notification triggers to test and fix

• Cron jobs — all scheduled background tasks should surface a notification on completion, failure, or when they produce a result the user should see
• Reminders — user-set reminders must fire a notification at the correct time
• Agent task completions — when a background agent task finishes, the user should be notified
• Scheduled messages / follow-ups — any scheduled outreach or follow-up should trigger a notification
• System events — e.g. low credits, session expiry warnings, update available

What to test

• Notifications fire for all cron job types (not just a subset)
• Reminder notifications fire at the correct scheduled time
• Notifications appear when the app is in the foreground
• Notifications appear when the app is in the background / minimised
• Notifications appear when the app is closed (system-level notification)
• Clicking a notification routes the user to the relevant context (correct thread, task, or reminder)
• Notification content is correct (title, body, timestamp)
• No duplicate notifications for the same event
• Missed notifications (app was closed) are surfaced on next app open

Known issues to investigate

• Cron-triggered notifications may not be reaching the frontend notification service
• Reminder notifications may be silently dropped if the scheduler gate is in a signed-out state
• Background notifications may not be firing on macOS due to missing entitlements or Focus mode

Acceptance Criteria

• All cron job types fire a notification on relevant completion/result
• All user reminders fire at the correct time in all app states (foreground, background, closed)
• Notification routing (click → correct screen) works for every notification type
• No duplicate or missing notifications in any tested scenario
• Test coverage added for notification dispatch paths