feat(pm/wiki): enable autosaving

If we edit the wiki but don't save, we'll lose our edits. We can enable
autosaving to let users use a setting to ... let that not happen! So
let's let that not happen!

packetmix/systems/wiki/wiki.nix

···
         $wgMFEnableMobilePreferences = true;
         wfLoadSkin( 'MinervaNeue' );
 
+        $wgEnableEditRecovery = true;
+
         $wgShowExceptionDetails = true;
         $wgDevelopmentWarnings = true;
       '';