fix: stop the duplicate "Create a New WP Note" form rendering at the bottom of My Notes

WordPress registers BOTH the parent menu's callback AND a submenu's
callback against the same page hook when they share a menu_slug, and
runs both in registration order. The My Notes submenu was passing
wp_notes_create_page as its callback (a separate bare-form renderer
used by the Tools-menu shortcut), so its output was being appended
below the main page content — appearing as a duplicate "Create a
New WP Note" form at the bottom of the My Notes page.

The submenu now passes an empty string as the callback — the
standard WP pattern when a submenu just relabels the parent (same
slug, same target page). Only the parent's wp_notes_page_callback
renders now.

The wp_notes_create_page function is unchanged and still serves
the Tools → My Notes shortcut at ?page=wp-notes-create.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wp-notes.php

@@ -177,16 +177,24 @@ function wp_notes_admin_menu() {
         3
     );
     
-    // "My Notes" — the main landing submenu (same slug as the parent
-    // menu, so clicking either WP Notes or My Notes lands on the same
-    // central dashboard: create form + active list + completed list).
+    // "My Notes" — the main landing submenu. Same slug as the parent
+    // menu so clicking either WP Notes or My Notes lands on the same
+    // central dashboard (the parent's wp_notes_page_callback already
+    // renders form + active list + completed list).
+    //
+    // CRITICAL: callback must be empty here. WordPress registers BOTH
+    // the parent's and the submenu's callbacks against the same page
+    // hook when slugs match, and runs them in order — passing
+    // wp_notes_create_page as the callback caused a duplicate
+    // "Create a New WP Note" form to render BELOW the main page
+    // content. Empty callback means only the parent's renderer fires.
     add_submenu_page(
         'wp-notes',                  // Parent slug
         'My Notes',                  // Page title (browser tab)
         'My Notes',                  // Menu label (sidebar)
         'manage_options',            // Capability
         'wp-notes',                  // Menu slug (matches parent → same page)
-        'wp_notes_create_page'       // Renderer
+        ''                           // Empty callback — see comment above
     );
 
     // Settings submenu