Add Focus Timer widget

[Alexismlg]

Fixes #410

Summary

Adds a Focus Timer widget — a focus/countdown timer you add from the widget picker. Pick a duration, optionally link it to one of your open windows, and start. When time is up the linked window shakes (via the public Window.shake()) and a gentle alarm rings until you press Stop.

Built following the starter-widget template and using only public APIs + runtime globals — no framework internals touched.

Features

• Duration presets (5 / 15 / 25 / 45 min) plus ±1-minute steppers (min 1 min, max 3 h).
• Optionally link the timer to any open window — that window shakes when time is up (looped Window.shake() until dismissed). Only currently-open windows are offered, and closing the linked window while the timer runs cancels it with a toast (the runtime listens for desktop-mode-window-closed).
• A Web Audio alarm chime that rings until dismissed — synthesized in the browser, no audio files bundled.
• Show / hide the remaining time while running.
• The timer keeps running across widget re-renders / re-docks (page-wide runtime singleton) and resumes across a page reload while still counting down (mirrored to ctx.storage).

Implementation

• src/plugins/focus-timer-widget/
  • index.ts — the view. Uses wpd-select (window picker) + wpd-checkbox-label (toggle) and native buttons, with __/sprintf from src/i18n.
  • timer.ts — a DOM-independent state machine (idle / running / paused / finished) held on window.__desktopModeFocusTimer so it survives re-mounts; persists to ctx.storage.
  • alarm.ts — Web Audio alarm; the AudioContext is primed on the Start click (a user gesture) so it can fire minutes later.
  • desktop.ts — a thin typed accessor over wp.desktop.windowManager to list + shake windows.
  • styles.css — layout only; overrides --desktop-mode-text / --desktop-mode-muted on the dark-glass card (same approach as the Note Pad widget) so the wpd-* components stay legible.
• includes/widgets/widget-focus-timer.php — registration (no REST, no server state, no external services).
• Wired into desktop-mode.php, vite.config.js (widget-focus-timer target), and package.json (build:widget-focus-timer + the build chain).

Pure client-side — no REST routes, no server state, no network calls.

Testing

• npm run build:widget-focus-timer, npm run typecheck, and npm run lint (on the new sources) all pass.
• Verified in wp-env: the widget appears in the picker, mounts cleanly (no console errors), countdown runs, and the linked-window shake + alarm + Stop flow works.

Notes / open questions

• Reduced-motion is respected (the finished-state shake/pulse animations drop to a static accent outline).
• Happy to add unit tests or a docs/example entry if the maintainers would like one for this widget.

[AllTerrainDeveloper]

By the PR description it already looks promising! Let me test it!

[AllTerrainDeveloper]

This is a great, I have tested it and it does what it promises. And also, I can see it as a core widget for Desktop Mode too :)

Timer.mov

[AllTerrainDeveloper]

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