feat(desktop): in-app prompt to restart for an update

The main process already showed a system notification when an update finished
downloading, and nothing in the renderer listened — so the only cue vanished on
its own and was missed by anyone not watching the desktop at that moment.

A prompt now stays in the window until it is acted on or dismissed, with the
restart wired to the install-update channel the preload already exposed.

Dismissing is 'not now', not 'never': a later version reopens the prompt, since
the version it refers to has changed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/web/src/i18n/locales/en.ts

@@ -56,6 +56,12 @@ export const en = {
   'accountMenu.copyId': 'Copy User ID',
   'accountMenu.copied': 'Copied',
 
+  // Desktop update
+  'update.ready': 'Update ready',
+  'update.readyVersion': 'Version {version} is ready to install.',
+  'update.restart': 'Restart to update',
+  'update.later': 'Later',
+
   // Custom emojis and stickers
   'expressions.title': 'Emojis & Stickers',
   'expressions.emojis': 'Emojis',