Add statistics route, permissions, and sidebar entry

- /statistics route and PagePaths.statistics
- Permission sets: viewer and admin can access /statistics
- Sidebar link with can_access_page check
- Plug and sidebar tests updated

lib/mv_web/components/layouts/sidebar.ex

@@ -88,6 +88,14 @@ defmodule MvWeb.Layouts.Sidebar do
         />
       <% end %>
 
+      <%= if can_access_page?(@current_user, PagePaths.statistics()) do %>
+        <.menu_item
+          href={~p"/statistics"}
+          icon="hero-chart-bar"
+          label={gettext("Statistics")}
+        />
+      <% end %>
+
       <%= if admin_menu_visible?(@current_user) do %>
         <.menu_group
           icon="hero-cog-6-tooth"