style: enhance plugin installation page and improve file selection handling

- Updated the plugin installation page to provide a console warning when no plugin file is selected, improving user feedback.
- Added a file tree for easier selection of plugin files, enhancing user experience during plugin installation.
- Adjusted the form layout for better alignment and consistency.

emhttp/plugins/dynamix.plugin.manager/PluginInstall.page

@@ -24,7 +24,7 @@ Tag="download"
       return;
     }
     file = file.trim();
-    if (!file) return;
+    if (!file) return console.warn('No plugin file selected');
     $.get('/plugins/dynamix.plugin.manager/include/ShowPlugins.php', {
       cmd: 'alert'
     }, function(data) {
@@ -47,11 +47,19 @@ Tag="download"
       e.preventDefault();
       installPlugin($('#plugin_file').val());
     });
+
+    $('#plugin_tree').fileTree({
+      root: '/boot/',
+      top: '/boot/',
+      filter:'plg',
+    }, function(file) {
+      $('#plugin_file').val(file);
+    });
   });
 </script>
 
 
-<form name="plugin_install" method="POST" target="progressFrame">
+<form class="max-w-20 mx-auto" name="plugin_install" method="POST" target="progressFrame">
   <p><strong>_(Enter URL of remote plugin file or local plugin file)_</strong></p>
   <div>
     <input type="text" name="file" id="plugin_file" maxlength="1024" value="">

emhttp/plugins/dynamix.plugin.manager/Plugins.page

@@ -145,7 +145,6 @@ function loadlist(id,check) {
 }
 $(function() {
   initlist();
-  $('#plugin_tree').fileTree({root:'/boot/',top:'/boot/',filter:'plg'}, function(file) {$('#plugin_file').val(file);});
   $('.tabs').append("<span id='checkall' class='status vhshift'><input type='button' value=\"_(Check For Updates)_\" onclick='openPlugin(\"checkall\",\"_(Plugin Update Check)_\",\":return\")' disabled></span>");
   $('.tabs').append("<span id='updateall' class='status vhshift' style='display:none;margin-left:12px'><input type='button' value=\"_(Update All Plugins)_\" onclick='updateList()'></span>");
   $('.tabs').append("<span id='removeall' class='status vhshift' style='display:none;margin-left:12px'><input type='button' value=\"_(Remove Selected Plugins)_\" onclick='removeList()'></span>");