adding playing time for a playlist

public/app.js

@@ -94,6 +94,27 @@ function formatTime(value) {
   return `${hours}:${minutes}:${seconds}`;
 }
 
+// Formats total playing time in the interface language, rounded to minutes.
+function formatPlayingTime(value) {
+  const totalMinutes = Number.isFinite(value) ? Math.max(0, Math.round(value / 60)) : 0;
+  const hours = Math.floor(totalMinutes / 60);
+  const minutes = totalMinutes % 60;
+  const language = window.RktTranslate.language();
+  const parts = [];
+  if (hours > 0) {
+    parts.push(new Intl.NumberFormat(language, {
+      style: "unit", unit: "hour", unitDisplay: "long",
+    }).format(hours));
+  }
+  if (minutes > 0 || hours === 0) {
+    parts.push(new Intl.NumberFormat(language, {
+      style: "unit", unit: "minute", unitDisplay: "long",
+    }).format(minutes));
+  }
+  const duration = new Intl.ListFormat(language, { style: "long", type: "conjunction" }).format(parts);
+  return t("playingTime", { duration });
+}
+
 // Replaces the current status message, using an empty string for no message.
 function setStatus(message) {
   elements.status.textContent = message || "";
@@ -504,7 +525,8 @@ function renderPlaylist(nextState) {
 
   elements.playlistEmpty.hidden = nextState.tracks.length > 0;
   const trackLabel = nextState.tracks.length === 1 ? "oneTrack" : "manyTracks";
-  elements.count.textContent = `${nextState.tracks.length} ${t(trackLabel)}`;
+  const tab = nextState.tabs[nextState.currentTab];
+  elements.count.textContent = `${nextState.tracks.length} ${t(trackLabel)}, ${formatPlayingTime(tab.duration)}`;
   elements.playlistClear.disabled = nextState.tracks.length === 0;
 }