fix: simplify LocalCluster startup to avoid timeout

Remove automatic application startup from LocalCluster.start_link
as it was causing timeouts. Applications are already being started
manually via RPC on each node after cluster creation.

Also convert prefix string to atom as required by LocalCluster 2.x.

Author: GSMLG-BOT

e2e_test/support/e2e_cluster_helper.ex

@@ -33,10 +33,10 @@ defmodule Concord.E2E.ClusterHelper do
     IO.puts("Starting #{node_count}-node cluster with prefix '#{prefix}'...")
 
     # Start cluster with LocalCluster 2.x API
+    # Note: Don't start applications here - they'll be started manually on each node
     {:ok, cluster} =
       LocalCluster.start_link(node_count,
-        prefix: prefix,
-        applications: [:ra, :telemetry, :concord]
+        prefix: String.to_atom(prefix)
       )
 
     # Get the node names