feat(channels): YouTube link on channel name + done checkmarks

- Channel name: middle-click opens the channel's YouTube page in a new tab
  (left-click still opens the in-app detail) plus an explicit external-link icon.
- recent/full sync badges show a check icon when the state is reached.
- New i18n key channels.row.openOnYouTube (HU/EN/DE).

frontend/src/components/Channels.tsx

@@ -4,6 +4,8 @@ import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import {
   ArrowDown,
   ArrowUp,
+  Check,
+  ExternalLink,
   Eye,
   EyeOff,
   History,
@@ -361,10 +363,11 @@ function SyncBadge({ ok, label, hint }: { ok: boolean; label: string; hint?: str
   return (
     <Tooltip hint={hint ?? ""}>
       <span
-        className={`text-[10px] px-1.5 py-0.5 rounded-full border ${
+        className={`inline-flex items-center gap-1 text-[10px] px-1.5 py-0.5 rounded-full border ${
           ok ? "border-accent/40 text-accent" : "border-border text-muted"
         }`}
       >
+        {ok && <Check className="w-3 h-3" />}
         {label}
       </span>
     </Tooltip>
@@ -393,6 +396,9 @@ function ChannelRow({
   onToggleTag: (tagId: number) => void;
 }) {
   const { t } = useTranslation();
+  const ytUrl = c.handle
+    ? `https://www.youtube.com/@${c.handle.replace(/^@/, "")}`
+    : `https://www.youtube.com/channel/${c.id}`;
   return (
     <div
       className={`glass-card glass-hover flex items-center gap-3 p-2.5 rounded-xl transition ${
@@ -418,9 +424,36 @@ function ChannelRow({
       />
 
       <div className="min-w-0 flex-1">
-        <button onClick={onView} className="text-sm font-semibold truncate hover:text-accent block max-w-full text-left">
-          {c.title ?? c.id}
-        </button>
+        <div className="flex items-center gap-1 max-w-full">
+          <button
+            onClick={onView}
+            onAuxClick={(e) => {
+              // Middle-click opens the channel's YouTube page in a new tab; left-click
+              // keeps opening the in-app channel detail.
+              if (e.button === 1) {
+                e.preventDefault();
+                window.open(ytUrl, "_blank", "noopener,noreferrer");
+              }
+            }}
+            onMouseDown={(e) => {
+              if (e.button === 1) e.preventDefault(); // suppress middle-click autoscroll
+            }}
+            className="text-sm font-semibold truncate hover:text-accent text-left min-w-0"
+          >
+            {c.title ?? c.id}
+          </button>
+          <Tooltip hint={t("channels.row.openOnYouTube")}>
+            <a
+              href={ytUrl}
+              target="_blank"
+              rel="noopener noreferrer"
+              className="text-muted hover:text-accent shrink-0"
+              aria-label={t("channels.row.openOnYouTube")}
+            >
+              <ExternalLink className="w-3.5 h-3.5" />
+            </a>
+          </Tooltip>
+        </div>
         <div className="flex items-center gap-2 text-[11px] text-muted">
           <span>{t("channels.row.stored", { count: c.stored_videos, formatted: c.stored_videos.toLocaleString() })}</span>
           {c.subscriber_count != null && <span>· {t("channels.row.subs", { count: c.subscriber_count, formatted: c.subscriber_count.toLocaleString() })}</span>}