refactor: full codebase overhaul — dead code removal, env validation, logger migration, date consolidation, Prisma schema cleanup, button consistency, useEffect deps, test coverage

- env.ts: added 10 missing Zod-validated env vars (imager, paypal currency, argon2/bcrypt params)
- Migrated 6 modules from process.env to validated env.* (auth, proxy-auth, paypal, password, redis, imager, moderation, alert, logger)
- Replaced console.warn/error with pino logger in 9 server-side modules
- Removed 50+ dead exports (SWF wrappers, coalesceHotelName, signIn, isStaff re-export, formatTimestamp, Skeleton/SkeletonCard, 4 unused housekeeping sections)
- Consolidated date formatting: 28 files migrated to shared formatDate() from @/lib/format-date
- Wired 4 radio/settings API routes through cached siteSettings service instead of raw Prisma queries
- Added getMany()/getAll() helpers to SiteSettings service
- Removed 88 dead Prisma model definitions (schema 2763→1846 lines)
- Created admin action-helper.ts with wrapAction() for standardized error handling
- Fixed useEffect dependency arrays in 4 data-heavy components
- Replaced raw btn CSS classes with shadcn Button component across admin pages
- Stripped dead i18n namespaces (common, pages.client) from all 22 translation files
- Removed 2 dead scripts (create-release.sh, check-local-imports.ts)
- Fixed knip.json configuration
- Added 7 new test suites: format-date, paypal, moderation, alert, webhook, action-helper, and fixed password.test.ts for env mocking
- All 358 tests passing across 72 test files
- TypeScript: 0 errors

src/messages/de.json

@@ -36,11 +36,6 @@
   "footer": {
     "copyright": "© {year} - {hotel} ist ein nicht-kommerzielles Bildungsprojekt"
   },
-  "common": {
-    "language": "Sprache",
-    "lightMode": "Heller Modus",
-    "darkMode": "Dunkler Modus"
-  },
   "pages": {
     "staff": {
       "title": "Team",
@@ -189,7 +184,7 @@
       "newsTitle": "Neueste Nachrichten",
       "newsSubtitle": "Frisch aus dem Hotel",
       "allNews": "Alle Nachrichten →",
-			"allUsers": "Community →",
+      "allUsers": "Community →",
       "noArticles": "Noch keine Artikel.",
       "noPhotos": "Noch keine Fotos.",
       "noUsers": "Keine Benutzer online",
@@ -664,7 +659,8 @@
       "securityTitle": "Sicherheit",
       "securitySubtitle": "Zwei-Faktor-Authentifizierung",
       "securityDescription": "Füge deinem Konto eine zweite Sicherheitsebene hinzu.",
-      "twoFactorLink": "Zwei-Faktor-Authentifizierung"},
+      "twoFactorLink": "Zwei-Faktor-Authentifizierung"
+    },
     "settings2fa": {
       "backToSettings": "← Einstellungen",
       "title": "Zwei-Faktor-Authentifizierung",
@@ -686,10 +682,10 @@
       "enableIntro": "Füge eine zweite Sicherheitsebene mit einer Authenticator-App hinzu.",
       "enable": "2FA aktivieren"
     },
-      "title": "Verbundene Konten",
-      "subtitle": "Verknüpfe ein Social-Media-Konto, damit du dich mit einem Klick anmelden kannst",
-      "connected": "Verbunden",
-      "unavailable": "Nicht verfügbar",
+    "title": "Verbundene Konten",
+    "subtitle": "Verknüpfe ein Social-Media-Konto, damit du dich mit einem Klick anmelden kannst",
+    "connected": "Verbunden",
+    "unavailable": "Nicht verfügbar",
     "login": {
       "title": "Anmelden",
       "subtitle": "Willkommen zurück — melde dich an, um das Hotel zu betreten.",
@@ -2775,21 +2771,6 @@
         }
       }
     },
-    "client": {
-      "title": "Nitro client",
-      "loading": "Loading client…",
-      "generatingTicket": "Generating SSO ticket…",
-      "connected": "Connected",
-      "welcome": "Welcome to {hotel}",
-      "openingClient": "Opening the client in a new tab…",
-      "fallbackLink": "If it doesn't open,",
-      "fallbackClick": "click here",
-      "errors": {
-        "unauthorized": "You need to be logged in to open the client.",
-        "generic": "Could not generate SSO ticket",
-        "loginRedirect": "Log in"
-      }
-    },
     "radioRequests": {
       "formTitle": "Submit a request",
       "formSubtitle": "Ask the DJ to play your favourite track",