Unified task registry — all scheduled jobs visible in Tasks app

[jaylfc]

Summary

All scheduled/background tasks created by any app must be registered in a central task system and visible in the Tasks app. No hidden background jobs.

Requirements

• Central task registry API that any app can register scheduled work with
• Tasks app shows ALL scheduled tasks across all apps: monitoring polls, release watches, ingest jobs, etc.
• Per-task controls: pause, resume, delete, change frequency
• Per-task info: source app, target item, last run, next run, status, frequency
• Apps that create scheduled tasks: Library (monitoring), Reddit Client (thread monitoring), YouTube Library (channel monitoring), GitHub Browser (release/issue monitoring), X Monitor (thread monitoring), Knowledge Pipeline (all ingest monitoring)

Architecture

• Backend: task registry in the existing scheduled task infrastructure
• When MonitorService polls an item, that poll schedule is a registered task
• When an app creates a "monitor this" action, it registers a task
• Tasks app reads from the registry and provides management UI
• Deleting a task from Tasks app stops the monitoring in the source app

Dependencies

• Existing Tasks app and backend
• MonitorService (already runs polls, needs to register them as visible tasks)