feat: blur booking codes setting + two-column settings page — closes #114

- New display setting "Blur Booking Codes" (off by default)
- When enabled, confirmation codes are blurred across all views
  (ReservationsPanel, DayDetailPanel, Transport detail modal)
- Hover or click reveals the code (click toggles on mobile)
- Settings page uses masonry two-column layout on desktop, single
  column on mobile (<900px)
- Fix hardcoded admin page title to use i18n key

client/src/i18n/translations/de.ts

@@ -139,6 +139,7 @@ const de: Record<string, string | { name: string; category: string }[]> = {
   'settings.temperature': 'Temperatureinheit',
   'settings.timeFormat': 'Zeitformat',
   'settings.routeCalculation': 'Routenberechnung',
+  'settings.blurBookingCodes': 'Buchungscodes verbergen',
   'settings.on': 'An',
   'settings.off': 'Aus',
   'settings.account': 'Konto',

client/src/i18n/translations/en.ts

@@ -139,6 +139,7 @@ const en: Record<string, string | { name: string; category: string }[]> = {
   'settings.temperature': 'Temperature Unit',
   'settings.timeFormat': 'Time Format',
   'settings.routeCalculation': 'Route Calculation',
+  'settings.blurBookingCodes': 'Blur Booking Codes',
   'settings.on': 'On',
   'settings.off': 'Off',
   'settings.account': 'Account',