Fix Credo Design in test support and member index test

Add aliases in fixtures, conn_case, data_case. Use aliases
in index_test.exs. Remove empty placeholder test files.

test/support/data_case.ex

@@ -16,6 +16,9 @@ defmodule Mv.DataCase do
 
   use ExUnit.CaseTemplate
 
+  alias Ecto.Adapters.SQL.Sandbox, as: Sandbox
+  alias Mv.Repo
+
   require Ash.Query
 
   using do
@@ -30,11 +33,11 @@ defmodule Mv.DataCase do
   end
 
   setup tags do
-    Mv.DataCase.setup_sandbox(tags)
+    setup_sandbox(tags)
     # Ensure "Mitglied" role exists for default role assignment to work in tests
     # Note: This runs in every test because each test runs in a sandboxed database.
     # The check is fast (single query) and idempotent (skips if role exists).
-    Mv.DataCase.ensure_default_role()
+    ensure_default_role()
     :ok
   end
 
@@ -43,8 +46,8 @@ defmodule Mv.DataCase do
   Returns the owner pid for use with Phoenix.Ecto.SQL.Sandbox.
   """
   def setup_sandbox(tags) do
-    pid = Ecto.Adapters.SQL.Sandbox.start_owner!(Mv.Repo, shared: not tags[:async])
-    on_exit(fn -> Ecto.Adapters.SQL.Sandbox.stop_owner(pid) end)
+    pid = Sandbox.start_owner!(Repo, shared: not tags[:async])
+    on_exit(fn -> Sandbox.stop_owner(pid) end)
     pid
   end