Handle database metrics collection gracefully during startup

Check if Repo process is started before attempting to collect PostgreSQL
metrics. This prevents the 'could not lookup Ecto repo' error message
during application startup when the periodic metrics collector runs
before the Repo is fully initialized.

The metrics collection now silently skips when the Repo isn't ready
and will succeed on subsequent runs once the Repo is started.

lib/aprsme/telemetry/database_metrics.ex

@@ -134,6 +134,18 @@ defmodule Aprsme.Telemetry.DatabaseMetrics do
   end
 
   defp do_collect_postgres_metrics do
+    # Check if Repo is started before collecting metrics
+    case Process.whereis(Aprsme.Repo) do
+      nil ->
+        # Repo not started yet, skip metrics collection silently
+        :ok
+
+      _pid ->
+        collect_database_metrics()
+    end
+  end
+
+  defp collect_database_metrics do
     # Database size
     case Aprsme.Repo.query("SELECT pg_database_size(current_database()) as size") do
       {:ok, %{rows: [[size]]}} ->