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/time.json

@@ -0,0 +1,10 @@
+{
+  "justNow": "gerade eben",
+  "secondsAgo": "vor {{count}} Sek.",
+  "minutesAgo": "vor {{count}} Min.",
+  "hoursAgo": "vor {{count}} Std.",
+  "daysAgo": "vor {{count}} T.",
+  "weeksAgo": "vor {{count}} Wo.",
+  "monthsAgo": "vor {{count}} Mon.",
+  "yearsAgo": "vor {{count}} J."
+}