feat: Ctrl+click deselect + global empty-area sweep

- Ctrl+click on selected item: deselect that item only
- Ctrl+click on empty space (via sweep start): deselect all items
- Ctrl+drag on empty space BETWEEN or BELOW tracks: creates
  sweep overlay scanning ALL tracks for intersecting items
- onDeselectItem handler + prop wired through WaveformLane
- Global onMouseDown on tracks container div for empty-area sweep

app/static/js/app.jsx

@@ -387,6 +387,7 @@ const WaveformLane = ({
   currentTime,
   getLocalAnchor,
   onClearLocalSelection,
+  onDeselectItem,
   onSetSelectionMode,
   onSetSelectionStart,
   onSetSelectionEnd,
@@ -1079,7 +1080,11 @@ const WaveformLane = ({
       if (hitItem && !e.altKey && !e.shiftKey) {
         e.preventDefault();
         e.stopPropagation();
-        if (onSectionItemDragStart) onSectionItemDragStart(track.id, hitItem.type, hitItem.id, time - hitItem.start, e.ctrlKey);
+        if (e.ctrlKey && selectedItemIds && selectedItemIds.has(hitItem.id)) {
+          if (onDeselectItem) onDeselectItem(hitItem.id);
+        } else {
+          if (onSectionItemDragStart) onSectionItemDragStart(track.id, hitItem.type, hitItem.id, time - hitItem.start, e.ctrlKey);
+        }
         return;
       }
 
@@ -1134,13 +1139,20 @@ const WaveformLane = ({
       if (clickedClip && (e.altKey || e.ctrlKey)) {
         e.preventDefault();
         e.stopPropagation();
+        if (e.ctrlKey && selectedItemIds) {
+          var clipCanonicalId = clickedClip.id === 'default' ? 'default_' + track.id : clickedClip.id;
+          if (selectedItemIds.has(clipCanonicalId)) {
+            if (onDeselectItem) onDeselectItem(clipCanonicalId);
+            return;
+          }
+        }
         if (onClipDragStart) {
           onClipDragStart(track.id, clickedClip.id, time - clickedClip.startTime, e.ctrlKey);
         }
         return;
       }
 
-      // Ctrl+Click on empty space: start sweep select
+      // Ctrl+Click on empty space: sweep select (deselect all via onSweepSelectStart)
       if (e.ctrlKey && !clickedClip && !hitItem) {
         e.preventDefault();
         e.stopPropagation();
@@ -11620,6 +11632,15 @@ const App = () => {
     };
   }, [zoom]);
 
+  // ── Deselect single item ──
+  const handleDeselectItem = itemId => {
+    setSelectedItemIds(prev => {
+      var next = new Set(prev);
+      next.delete(itemId);
+      return next;
+    });
+  };
+
   // ── Sweep Select ──
   const handleSweepSelectStart = (trackId, startTime) => {
     isSweepingRef.current = true;
@@ -11902,7 +11923,9 @@ const App = () => {
     const handleMouseUp = () => {
       if (!isSweepingRef.current) return;
       isSweepingRef.current = false;
+      sweepTrackIdRef.current = null;
       const sweep = sweepSelectRef.current;
+      sweepSelectRef.current = null;
       if (sweep) {
         const start = Math.min(sweep.startTime, sweep.endTime);
         const end = Math.max(sweep.startTime, sweep.endTime);
@@ -16456,7 +16479,19 @@ const App = () => {
         borderRight: '1px solid #f59e0b'
       }
     })), /*#__PURE__*/React.createElement("div", {
-      className: "flex-1 flex flex-col divide-y divide-[#141414] relative bg-[#111111] min-h-full"
+      className: "flex-1 flex flex-col divide-y divide-[#141414] relative bg-[#111111] min-h-full",
+      onMouseDown: e => {
+        if (e.ctrlKey && !e.shiftKey && !e.altKey && e.button === 0) {
+          const wrapper = timelineWrapperRef.current;
+          if (wrapper) {
+            const rect = wrapper.getBoundingClientRect();
+            const sl = wrapper.scrollLeft;
+            const raw = Math.max(0, (e.clientX - rect.left + sl) / zoom - leadInMargin);
+            const time = snapValue !== 'free' ? snapTime(raw, snapValue, bpm) : raw;
+            handleSweepSelectStart(null, time);
+          }
+        }
+      }
     }, activeTracks.map((track, idx) => {
       const isSelected = selectedTrackId === track.id;
       const autoHeight = track.height || (track.isArmed ? 164 : 140);
@@ -16486,6 +16521,7 @@ const App = () => {
          markers: track.markers,
          onTrackLaneMouseDown: handleTrackLaneMouseDown,
          onSweepSelectStart: handleSweepSelectStart,
+         onDeselectItem: handleDeselectItem,
         onContextMenu: handleContextMenu,
         onClipDragStart: handleClipDragStart,
         onClipStretchStart: handleClipStretchStart,