feat(updater): polish macOS update modal with countdown, trust badges, clean button states

- Footer buttons are now state-dependent: Skip / Remind later only show
  during idle; the install button no longer leaves a gap when it
  disappears, and "Remind later" stops shifting between states
- Post-install on macOS shows a 3-second visible restart countdown with
  a "Restart now" button instead of triggering an invisible relaunch
  that sometimes didn't actually fire
- macOS idle state now explains the in-place update model (no DMG
  download) and shows trust badges: "Notarized by Apple" + "Signature
  verified" as an at-a-glance trust signal
- Download state during install hides all secondary buttons so the
  progress bar stands alone
- New i18n keys in en/de; fr/nl/zh/nb/ru/es fall back to the English
  defaultValue until translated in a follow-up

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/en.ts

@@ -409,6 +409,15 @@ export const enTranslation = {
     updaterAurHint: 'Install the update via AUR:',
     updaterErrorMsg: 'Download failed',
     updaterRetryBtn: 'Retry',
+    updaterInstallNow: 'Install now',
+    updaterMacReadyTitle: 'Ready to install',
+    updaterMacReady: 'The update downloads, verifies and applies in place — no DMG needed. The app restarts automatically when done.',
+    updaterTrustNotarized: 'Notarized by Apple',
+    updaterTrustSignature: 'Signature verified',
+    updaterMacDoneTitle: 'Update installed',
+    updaterRestartingIn: 'Restarting in {{n}}s…',
+    updaterRestarting: 'Restarting…',
+    updaterRestartNow: 'Restart now',
     durationHoursMinutes: '{{hours}}h {{minutes}}m',
     durationMinutesOnly: '{{minutes}}m',
     updaterOpenGitHub: 'Open on GitHub',