Add scheduled agent work

[MattFlower]

Summary

• add a Scheduled Work backend manager that persists tasks/runs and executes Claude, Pi, and Codex non-interactively
• support once, interval, and five-field cron schedules with live run status, cancellation, logs, and results
• add a Scheduled Work view plus sidebar/menu/RPC wiring and changelog entry

Verification

• bun test
• bun build src/views/main/components/scheduled-work/ScheduledWorkView.tsx --external react --external react/jsx-runtime --external electrobun/view --external zustand --external eruda --outdir /tmp/tempest-scheduled-build
• bun build src/bun/scheduled-work/scheduled-work-manager.ts --target bun --external electrobun/bun --outdir /tmp/tempest-scheduled-build-bun
• Computer Use smoke: created a cron Codex task, ran it manually, observed exit 0/log output, edited it, and paused it

Notes

• bun x tsc --noEmit still fails on existing unrelated repo issues: missing @types/three, Dirent typing mismatches, browser JSX intrinsic, onboarding fallback, and existing rpc-client errors.