Revert canvas parent z-index to avoid masking sidebar

Keep only the timeline z-index: 1000 bump. Setting z-index on the
canvas parent would create a stacking context that paints over the
sidebar panel, blocking interaction.

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

js/snapshot_manager.js

@@ -1413,15 +1413,11 @@ function buildTimeline() {
         return;
     }
 
-    // Ensure parent is positioned so absolute children work, and
-    // sits above the ComfyUI sidebar (z-index: 10) in the stacking order
+    // Ensure parent is positioned so absolute children work
     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");