Fix Now Processing panel never showing once the queue backlog exceeds ~500 jobs

The main queue list sorts by created_at desc and caps at 500 rows, but the FIFO
worker processes oldest-first — with a large backlog the actually-running job
was routinely outside that window and never reached the frontend at all.
Fetch it via a dedicated /transcode/queue/running endpoint instead.

frontend/src/pages/TranscodeQueue.jsx

@@ -15,6 +15,7 @@ const STATUS_COLORS = {
 export default function TranscodeQueue() {
   const [jobs, setJobs] = useState([]);
   const [stats, setStats] = useState({ pending: 0, running: 0, done: 0, failed: 0, cancelled: 0, paused: false, auto_transcode: "off" });
+  const [runningJob, setRunningJob] = useState(null);
   const [loading, setLoading] = useState(false);
 
   const load = async () => {
@@ -25,19 +26,24 @@ export default function TranscodeQueue() {
       setStats(s.data);
     } finally { setLoading(false); }
   };
-  useEffect(() => { load(); }, []);
+  // The running job can be far outside the main list's created_at-desc/500-row window once
+  // there's a large backlog (the FIFO worker processes oldest-first), so it's fetched separately
+  // rather than derived from `jobs`.
+  const loadRunning = async () => {
+    try { const { data } = await api.get("/transcode/queue/running"); setRunningJob(data); }
+    catch { /* ignore transient poll failures */ }
+  };
+  useEffect(() => { load(); loadRunning(); }, []);
 
   // Poll while jobs are active — faster while something is actually running so the
   // progress bar feels live, slower while only pending jobs are waiting.
   useEffect(() => {
-    const running = jobs.some((j) => j.status === "running");
     const pending = jobs.some((j) => j.status === "pending");
-    if (!running && !pending) return;
-    const t = setInterval(load, running ? 2000 : 4000);
+    if (!runningJob && !pending) return;
+    const t = setInterval(() => { load(); loadRunning(); }, runningJob ? 2000 : 4000);
     return () => clearInterval(t);
-  }, [jobs]);
+  }, [jobs, runningJob]);
 
-  const runningJob = jobs.find((j) => j.status === "running");
   const listedJobs = jobs.filter((j) => j.status !== "running");
 
   const cancel = async (id) => {