Add multisite support for admin page

Is your enhancement related to a problem? Please describe.

The admin screen from #32 and the plugin action link from #36 are not fully working in multisite yet, or rather, they are limited to the individual site's WP Admin UI. We should expand that so that the same admin screen works in the Network Admin UI as well.

This is particularly critical, since on some multisite configurations regular administrators are not allowed to control plugins.

Acceptance Criteria

• The admin page class from #32 should be expanded to also add the same admin screen on the network_admin_menu action hook.
  • The admin page added can behave the same way for now, but since the "Tools" menu does not exist in the Network Admin, we should add the screen in the "Settings" menu there (i.e. use add_submenu_page() with settings.php).
• The plugin action links from #36 should be expanded to also show up in the Network Admin via the network_admin_plugin_action_links filter.
  • Particular attention has to be paid to the URL, since the page lives under settings.php here (instead of options-general.php in the regular WP Admin).

Test Coverage

• Ensure the admin page is added propertly when using the Network Admin specific action.
• Ensure the plugin link is added properly when using the Network Admin specific filter.

Start with the admin page class from #32 and the plugin action links from #36. Review the existing regular-admin hooks, then compare the requested network_admin_menu and network_admin_plugin_action_links behavior, including settings.php URLs. Done means both network-admin paths work and have coverage for their page and link output.