feat: Datafields page, merge fee types into membership_fee_settings, sidebar

- Add /admin/datafields (DatafieldsLive) for member and custom field config
- Remove Memberdata block from GlobalSettingsLive
- Router: drop /membership_fee_types, add new_fee_type and edit_fee_type under membership_fee_settings
- MembershipFeeSettingsLive: fee types table, collapsible examples; Index links updated
- PagePaths: admin_datafields, admin_import; remove membership_fee_types
- Sidebar: order and labels (Basic settings, Datafields, Membership fee settings, Import, Users, Roles)
- Gettext: German translations for sidebar and OIDC
- Tests: datafields and fee routes, permission and form tests updated

test/mv_web/live/global_settings_live_test.exs

@@ -64,21 +64,5 @@ defmodule MvWeb.GlobalSettingsLiveTest do
 
       assert html =~ "must be present"
     end
-
-    test "displays Memberdata section", %{conn: conn} do
-      {:ok, _view, html} = live(conn, ~p"/settings")
-
-      assert html =~ "Memberdata" or html =~ "Member Data"
-    end
-
-    test "displays flash message after member field visibility update", %{conn: conn} do
-      {:ok, view, _html} = live(conn, ~p"/settings")
-
-      # Simulate member field visibility update
-      send(view.pid, {:member_field_visibility_updated})
-
-      # Check for flash message
-      assert render(view) =~ "updated" or render(view) =~ "success"
-    end
   end
 end