fix: multi-item drag mousemove didn't handle clips

The multi-item drag mousemove handler only processed
info.type === 'section' and 'midiItem'. Added 'clip' support
(midClips slice + findIndex + update).

app/static/js/app.jsx

@@ -11818,6 +11818,7 @@ const App = () => {
             var delta = newStart - dragOrigStart;
             var midSections = (t.sections || []).slice();
             var midMidis = (t.midiItems || []).slice();
+            var midClips = (t.clips || []).slice();
             Object.keys(drag.multiIds).forEach(function(mid) {
               var info = drag.multiIds[mid];
               var newVal = info.start + delta;
@@ -11827,9 +11828,12 @@ const App = () => {
               } else if (info.type === 'midiItem') {
                 var idx = midMidis.findIndex(function(m) { return m.id === mid; });
                 if (idx >= 0) midMidis[idx] = { ...midMidis[idx], startTime: Math.max(0, newVal) };
+              } else if (info.type === 'clip') {
+                var idx = midClips.findIndex(function(c) { return c.id === mid; });
+                if (idx >= 0) midClips[idx] = { ...midClips[idx], startTime: Math.max(0, newVal) };
               }
             });
-            return { ...t, sections: midSections, midiItems: midMidis };
+            return { ...t, sections: midSections, midiItems: midMidis, clips: midClips };
           }
           const items = drag.itemType === 'section' ? (t.sections || []) : (t.midiItems || []);
           const updatedItems = items.filter(it => it.id !== drag.itemId);