[#1287] feat(frontend): add audible sound alert toggle and browser push notifications

[ToryMic]

Summary

High and critical alerts only ever rendered inside the notifications drawer, so an operator who switched to another window never noticed a tripped circuit breaker or a reserve mismatch. This PR adds audible and out-of-tab alerting for those two priorities.

What was added

• useAlertChime — chimes via the Web Audio API. Critical gets a descending two-tone siren, high a single blip, so the two are distinguishable without looking. A single AudioContext is created lazily and reused (browsers cap how many a page may hold), and each oscillator is disconnected on ended so nodes don't accumulate over a long shift.
• useDesktopNotifications — native notifications via the Web Notifications API, dispatched only while the document is hidden. If the operator is already looking at the tab, a native popup would duplicate the drawer.
• useAlertNotifier — watches the notification store and fires either channel for newly arrived high/critical alerts.
• Drawer switches for both channels, persisted through the existing soundEnabled and notificationsEnabled user preferences, which were defined but previously unused.

Browser constraints, surfaced rather than swallowed

• The audio switch arms the AudioContext in the same click. Browsers keep it suspended until a user gesture, so without this the first chime is silent. Until then the drawer tells the operator to tap once.
• Notification permission is requested only on the enabling gesture — browsers reject prompts that aren't user-initiated.
• A denied permission shows how to unblock it in browser settings.
• If the browser has no Web Audio API, the switch is disabled with an explanation rather than silently doing nothing.

Avoiding noise

The store is seeded with existing notification ids on mount, so a page reload does not replay every historical alert as a siren. Each id fires at most once, and medium/low priorities stay silent.

Testing

• 31 new tests: useAlertChime.test.ts (10), useAlertNotifier.test.ts (9), NotificationsDrawer.alerts.test.tsx (12)
• All pass; the existing 10 NotificationsDrawer.test.tsx tests still pass
• eslint and tsc --noEmit clean on every changed file

Pre-existing baseline failures (not touched here): the frontend suite on main already fails with 76 tests across 15 files. That count is identical before and after this branch, so this adds no new failures. .github/workflows/ci.yml and docker.yml also fail to parse on main (invalid ${{ runner.temp }} in job-level env and ${{ id.meta.* }}), which is an upstream issue I have left alone.

Reviewer notes

• No backend changes: the priorities (critical / high) already exist on the notification store, so the feature needed no new data.
• There is a second, older NotificationContext that plays /notification-sound.mp3 via new Audio(). It uses a different Notification type with no priority field and a separate storage key. I did not touch it — consolidating the two notification systems looked out of scope, but it is worth a follow-up issue since it means the two systems can disagree about what has alerted.

Closes #1287

[drips-wave]

@ToryMic Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits