Auto-save every video you play for offline, with a Settings switch

frontend/views-core.js

@@ -844,6 +844,13 @@ async function renderSettings() {
     <div class="set-group">
       <div class="set-group-title">Offline cache</div>
       <div class="set-row"><span>App &amp; features</span><small id="offlineAssetStatus" role="status">Checking offline readiness…</small></div>
+      <label class="set-row">
+        <span>
+          Auto-save videos I play
+          <small>Every video you open is kept on this device in the background, so it plays offline later.</small>
+        </span>
+        <input id="setAutoSavePlayed" type="checkbox" ${data.settings.autoSavePlayed !== false ? 'checked' : ''} />
+      </label>
       <label class="set-row">
         <span>
           Auto-save playlist videos
@@ -1116,6 +1123,10 @@ async function renderSettings() {
     persist();
     Notes.refreshFlags();
   });
+  $('setAutoSavePlayed').addEventListener('change', (e) => {
+    data.settings.autoSavePlayed = e.target.checked;
+    persist();
+  });
   $('setAutoPreload').addEventListener('change', (e) => {
     data.settings.autoPreload = e.target.checked;
     persist();