feat: timed warm-up scheduling

[YaphetSf]

Summary

Adds a Timed warm-up mode so you can pick specific times of day to warm up
all accounts, instead of relying only on the existing window-reset auto warm-up.
This gives control over when your 5-hour usage windows start rather than
letting them drift.

What's new

• Timed warm-up control in the main window header — a popover to toggle the
  feature on/off and manage a list of HH:MM times (e.g. 08:00, 13:00,
  18:00).
• At each scheduled time the app warms all accounts, skipping any whose
  weekly limit is exhausted.
• A global enabled flag + the list of times are persisted in localStorage.
• A 30s scheduler fires each time once per day. A missed time (e.g. while
  the machine is asleep) is skipped rather than warmed late at the wrong moment.

Notes

• The scheduler runs inside the main app window, so the app must stay running
  (it can live in the tray) and the machine awake. The README documents using
  macOS caffeinate for this.
• Existing manual and automatic (window-reset) warm-up are unchanged; timed
  warm-up is independent and can be used alongside them.
• Frontend-only change (no Rust touched). tsc, pnpm build, and
  cargo fmt --check all pass.

Docs

Adds a Warm-Up section to the README explaining the manual / automatic /
timed modes.

[emreertunc]

I found a functional blocker, so I don’t think this is ready to approve yet.

The timed scheduler runs checkTimedWarmup() immediately when the effect mounts. If the current minute matches a configured time, it marks that time as fired before calling runTimedWarmup(). But runTimedWarmup() reads targets from accountsRef.current, which can still be empty during initial app load. In that case no accounts are warmed, but the scheduled time is still considered fired for the day, so opening or reloading the app during the scheduled minute can silently skip the timed warm-up.

Relevant code: src/App.tsx, around runTimedWarmup and the timed scheduler effect.

There is also a smaller related issue: TIMED_WARMUP_LEDGER_STORAGE_KEY is defined but unused, so the once-per-day fire ledger is only in memory. A reload or reopen during the same scheduled minute can allow duplicate firing.

Also, README has a small typo: sinlge should be single.