i18n(a11y): translate the modal + Welcome close buttons and the feed fallback (C-3.22)

House policy is HU+EN for every user-facing string. Modal's shared close button was a
hardcoded title="Close" (in every modal) — now t("common.close") + an aria-label.
Welcome's lightbox close aria-label and Feed's "this video" notification fallback are
translated too (new feed.thisVideo, HU+EN). The other Close hardcodes the review
listed were already fixed since.

frontend/src/components/Feed.tsx

@@ -255,7 +255,7 @@ export default function Feed({
               meta: {
                 kind: "video-hidden",
                 videoId: id,
-                title: v?.title ?? "this video",
+                title: v?.title ?? i18n.t("feed.thisVideo"),
                 channelId: v?.channel_id ?? "",
                 channelName: v?.channel_title ?? "",
               },
@@ -270,7 +270,7 @@ export default function Feed({
               meta: {
                 kind: "video-watched",
                 videoId: id,
-                title: v?.title ?? "this video",
+                title: v?.title ?? i18n.t("feed.thisVideo"),
                 channelId: v?.channel_id ?? "",
                 channelName: v?.channel_title ?? "",
               },

frontend/src/components/Modal.tsx

@@ -1,5 +1,6 @@
 import { useEffect, useRef, type ReactNode } from "react";
 import { createPortal } from "react-dom";
+import { useTranslation } from "react-i18next";
 import { X } from "lucide-react";
 import { useBackToClose } from "../lib/history";
 
@@ -27,6 +28,7 @@ export default function Modal({
   children: ReactNode;
   maxWidth?: string;
 }) {
+  const { t } = useTranslation();
   // Browser/mouse Back closes the topmost modal instead of navigating away.
   useBackToClose(onClose);
 
@@ -76,7 +78,8 @@ export default function Modal({
           <h2 className="text-lg font-semibold leading-snug">{title}</h2>
           <button
             onClick={onClose}
-            title="Close"
+            title={t("common.close")}
+            aria-label={t("common.close")}
             className="shrink-0 p-1.5 rounded-lg text-muted hover:text-fg hover:bg-surface transition"
           >
             <X className="w-4 h-4" />

frontend/src/components/Welcome.tsx

@@ -212,6 +212,7 @@ function Preview({
 // Full-size image viewer: a dimmed, blurred backdrop with the screenshot fit to the viewport
 // (aspect ratio preserved via object-contain). Closes on backdrop click, the ✕, or Escape.
 function Lightbox({ src, label, onClose }: { src: string; label: string; onClose: () => void }) {
+  const { t } = useTranslation();
   useEffect(() => {
     const onKey = (e: KeyboardEvent) => {
       if (e.key === "Escape") onClose();
@@ -235,7 +236,7 @@ function Lightbox({ src, label, onClose }: { src: string; label: string; onClose
       <button
         type="button"
         onClick={onClose}
-        aria-label="Close"
+        aria-label={t("common.close")}
         className="absolute top-4 right-4 p-2 rounded-full glass-card glass-hover text-fg"
       >
         <X className="w-5 h-5" />

frontend/src/i18n/locales/en/feed.json

@@ -45,6 +45,7 @@
   "undo": "Undo",
   "markedWatchedNamed": "Marked watched “{{title}}”",
   "markedWatched": "Marked watched",
+  "thisVideo": "this video",
   "unwatch": "Unwatch",
   "source": {
     "label": "Source",

frontend/src/i18n/locales/hu/feed.json

@@ -45,6 +45,7 @@
   "undo": "Visszavonás",
   "markedWatchedNamed": "Megnézettnek jelölve: „{{title}}”",
   "markedWatched": "Megnézettnek jelölve",
+  "thisVideo": "ez a videó",
   "unwatch": "Megnézés visszavonása",
   "source": {
     "label": "Forrás",