Fix timeline bar hidden behind sidebar by raising z-index

ComfyUI's sidebar container uses z-index: 10. The timeline was at the
same level and lost in the stacking order. Bump timeline to z-index
1000 and set z-index 20 on the canvas parent so it forms a stacking
context above the sidebar.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

js/snapshot_manager.js

@@ -891,7 +891,7 @@ const CSS = `
     display: flex;
     align-items: center;
     padding: 0 16px;
-    z-index: 10;
+    z-index: 1000;
     pointer-events: auto;
 }
 .snap-timeline-track {
@@ -1413,11 +1413,15 @@ function buildTimeline() {
         return;
     }
 
-    // Ensure parent is positioned so absolute children work
+    // Ensure parent is positioned so absolute children work, and
+    // sits above the ComfyUI sidebar (z-index: 10) in the stacking order
     const parentPos = getComputedStyle(canvasParent).position;
     if (parentPos === "static") {
         canvasParent.style.position = "relative";
     }
+    if (!canvasParent.style.zIndex) {
+        canvasParent.style.zIndex = "20";
+    }
 
     // Create root element
     const bar = document.createElement("div");