fix(workflow): elevate the connection preview edge with the rest

It renders highlighted — its data carries `isConnectedToSelection` — but it was
the one call site left taking a depth tier, so the line being drawn could be
crossed by an ordinary edge in a deeper container. Highlighted now means
elevated with no exception.

Also drop the export on the highlighted tier: nothing outside the module reads
it, and the band's tiers are an implementation detail of `getEdgeZIndex`.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx

@@ -4529,7 +4529,12 @@ const WorkflowContent = React.memo(
           target: CONNECTION_BLOCK_SELECTOR_NODE_ID,
           targetHandle: 'target',
           type: 'workflowEdge',
-          zIndex: getEdgeZIndex(sourceParentNode ? (sourceParentNode.zIndex ?? 0) : undefined),
+          /* Rendered highlighted (`isConnectedToSelection` below), so it is
+             elevated like any other highlighted edge — the preview line is the
+             one the user is currently drawing. */
+          zIndex: getEdgeZIndex(sourceParentNode ? (sourceParentNode.zIndex ?? 0) : undefined, {
+            isHighlighted: true,
+          }),
           focusable: false,
           deletable: false,
           reconnectable: false,

packages/workflow-renderer/src/canvas-layers.ts

@@ -37,7 +37,7 @@ const EDGE_Z_DEPTH_MAX = 18
  * own endpoints; a line belongs behind cards, knobs and the action-bar swell
  * whether or not it is highlighted.
  */
-export const EDGE_Z_HIGHLIGHTED = 19
+const EDGE_Z_HIGHLIGHTED = 19
 export const EDGE_Z_MAX = 20
 export const BLOCK_Z_BASE = 21
 export const CONTAINER_CHILD_Z_BASE = 1000