design(chat): fix z-index stacking to ensure collapse button floats above dashboard pane

vibn-frontend/components/vibn-chat/chat-panel.tsx

@@ -2505,6 +2505,7 @@ export function ChatPanel({
                 flexDirection: "row",
                 minHeight: 0,
                 minWidth: 0,
+                position: "relative", // Ensure relative positioning for z-index stacking context
               }}
             >
               <div
@@ -2520,7 +2521,7 @@ export function ChatPanel({
                   transition: "width 0.2s ease-in-out",
                   overflow: "visible", // Changed from hidden to visible so the collapse button can hang over the edge
                   position: "relative",
-                  zIndex: 40,
+                  zIndex: 40, // High z-index to pop over the right panel
                 }}
               >
                 {isChatMinimized ? (
@@ -2606,6 +2607,8 @@ export function ChatPanel({
                   background: "#faf8f5",
                   display: "flex",
                   flexDirection: "column",
+                  position: "relative",
+                  zIndex: 10, // Lower z-index so the collapse button stays on top
                 }}
               >
                 {artifactSlot}