fix: don't reset desktop notification preference on startup

[Jord38]

Summary

• What: Changed refreshPermission() in NotificationStore to only disable notifications when platform permission is revoked, instead of unconditionally setting the value
• Why: On desktop (Electron), isGranted() always returns true, so the preference was overwritten to "on" every app restart
• Notes for reviewers: kiss kiss

How to verify

1. Desktop: disable notifications in settings, close and reopen the app
2. Desktop: enable notifications, close and reopen
3. Web: with notifications disabled in-app and browser permission granted, reload

Tests

• Added/updated tests (where it makes sense)
• Unit tests: no existing tests on notificationstore
• Integration tests: n/a
• Manual verification: tested on desktop and web

Checklist

• PR targets canary
• PR title follows Conventional Commits (mostly lowercase)
• CI is green (or I’m actively addressing failures)
• CLA signed (the bot will guide you on first PR)

Screenshots / recordings (UI changes)

n/a

[CLAassistant]

All committers have signed the CLA.

[Jord38]

Addresses #115