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/components/ErrorBoundary.tsx

@@ -1,4 +1,5 @@
 import { Component, type ReactNode } from "react";
+import i18n from "../i18n";
 import { notify } from "../lib/notifications";
 
 interface Props {
@@ -20,8 +21,8 @@ export default class ErrorBoundary extends Component<Props, State> {
   componentDidCatch(error: Error) {
     notify({
       level: "fatal",
-      title: "Something broke",
-      message: error.message || "Unexpected error",
+      title: i18n.t("errors.boundary.notifTitle"),
+      message: error.message || i18n.t("errors.boundary.notifMessage"),
       requiresInteraction: true,
     });
   }
@@ -31,13 +32,13 @@ export default class ErrorBoundary extends Component<Props, State> {
       return (
         <div className="min-h-screen grid place-items-center text-muted p-6 text-center">
           <div>
-            <div className="text-lg font-semibold text-fg mb-1">Something went wrong.</div>
-            <div className="text-sm mb-3">The app hit an unexpected error.</div>
+            <div className="text-lg font-semibold text-fg mb-1">{i18n.t("errors.boundary.title")}</div>
+            <div className="text-sm mb-3">{i18n.t("errors.boundary.subtitle")}</div>
             <button
               onClick={() => location.reload()}
               className="text-accent hover:underline text-sm font-semibold"
             >
-              Reload
+              {i18n.t("errors.boundary.reload")}
             </button>
           </div>
         </div>