fix: trace page crash - detected_at → changed_at to match ConfigChangeEvent schema

lib/towerops/trace.ex

@@ -331,8 +331,8 @@ defmodule Towerops.Trace do
 
     ConfigChangeEvent
     |> where(device_id: ^device_id)
-    |> where([c], c.detected_at >= ^since)
-    |> order_by(desc: :detected_at)
+    |> where([c], c.changed_at >= ^since)
+    |> order_by(desc: :changed_at)
     |> limit(10)
     |> Repo.all()
   end

lib/towerops_web/live/trace_live/index.html.heex

@@ -437,7 +437,7 @@
                       {Map.get(change, :changed_sections, []) |> Enum.join(", ")}
                     </span>
                     <span class="text-xs text-gray-500">
-                      {format_relative_time(change.detected_at)}
+                      {format_relative_time(change.changed_at)}
                     </span>
                   </div>
                   <div