feat(i18n): translate remaining components (HU/EN/DE)

Feed, VideoCard, Sidebar, PlayerModal, Channels, Stats, SettingsPanel,
OnboardingWizard, NotificationCenter, Toaster, ErrorBoundary and the relativeTime
helper are now fully translated in Hungarian, English and German, each with its own
locale area file (auto-loaded). Key parity verified across all three languages.

frontend/src/i18n/locales/de/notifications.json

@@ -0,0 +1,19 @@
+{
+  "title": "Benachrichtigungen",
+  "clearAll": "Alle löschen",
+  "clear": "Löschen",
+  "empty": "Noch keine Benachrichtigungen.",
+  "actionNeeded": "Aktion erforderlich",
+  "dismiss": "Schließen",
+  "findInFeed": "Im Feed finden",
+  "unhide": "Einblenden",
+  "unwatch": "Nicht angesehen",
+  "unhidden": "Eingeblendet „{{title}}”",
+  "unwatched": "Als nicht angesehen markiert „{{title}}”",
+  "time": {
+    "justNow": "gerade eben",
+    "minutes": "vor {{count}} Min.",
+    "hours": "vor {{count}} Std.",
+    "days": "vor {{count}} T."
+  }
+}