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/en/notifications.json

@@ -0,0 +1,19 @@
+{
+  "title": "Notifications",
+  "clearAll": "Clear all",
+  "clear": "Clear",
+  "empty": "No notifications yet.",
+  "actionNeeded": "Action needed",
+  "dismiss": "Dismiss",
+  "findInFeed": "Find in feed",
+  "unhide": "Unhide",
+  "unwatch": "Unwatch",
+  "unhidden": "Unhidden “{{title}}”",
+  "unwatched": "Unwatched “{{title}}”",
+  "time": {
+    "justNow": "just now",
+    "minutes": "{{count}}m ago",
+    "hours": "{{count}}h ago",
+    "days": "{{count}}d ago"
+  }
+}