feat(web): add font size setting

- Add Settings > Display > Font Size selector (80/90/100/110/120%)
- Persist preference (hapi-font-scale) and apply globally via --app-font-scale
- Normalize main UI typography to match Settings

web/src/lib/locales/en.ts

@@ -234,6 +234,8 @@ export default {
   'settings.title': 'Settings',
   'settings.language.title': 'Language',
   'settings.language.label': 'Language',
+  'settings.display.title': 'Display',
+  'settings.display.fontSize': 'Font Size',
   'settings.voice.title': 'Voice Assistant',
   'settings.voice.language': 'Voice Language',
   'settings.voice.autoDetect': 'Auto-detect',