docs: drop Advanced from nav and hide its pages (SD-2873)

The Advanced group was turning into a junk drawer of paths we're
walking away from in v2 of the editor. Hide all of them from nav
while keeping the files reachable by direct URL for existing
inbound links:

- SuperEditor (4 pages): the Document API on SuperDoc covers the
  headless story now (editor.doc.* gives full programmatic access
  without instantiating SuperEditor directly).
- Headless toolbar + examples: superdoc/ui will eventually offer
  full toolbar control across frameworks (tracked in SD-2874);
  hiding now so we don't teach the deprecated path.

Existing redirects keep old URLs working; the pages just don't
appear in the sidebar.

Author: caio-pizzol

apps/docs/advanced/headless-toolbar-examples.mdx

@@ -1,5 +1,6 @@
 ---
 title: Headless Toolbar Examples
+hidden: true
 sidebarTitle: Examples
 keywords: "toolbar examples, vue toolbar, svelte toolbar, custom toolbar examples"
 ---

apps/docs/advanced/headless-toolbar.mdx

@@ -1,5 +1,6 @@
 ---
 title: Headless Toolbar
+hidden: true
 sidebarTitle: Headless
 keywords: "headless toolbar, custom toolbar, toolbar api, createHeadlessToolbar, toolbar state, toolbar commands"
 ---

apps/docs/advanced/supereditor/configuration.mdx

@@ -1,5 +1,6 @@
 ---
 title: Configuration
+hidden: true
 keywords: "supereditor config, editor configuration, prosemirror setup, document editor options, advanced config"
 ---
 

apps/docs/advanced/supereditor/events.mdx

@@ -1,5 +1,6 @@
 ---
 title: Events
+hidden: true
 keywords: "supereditor events, editor lifecycle, document events, editor callbacks, editor hooks"
 ---
 

apps/docs/advanced/supereditor/methods.mdx

@@ -1,5 +1,6 @@
 ---
 title: Methods
+hidden: true
 keywords: "supereditor methods, editor commands, document manipulation, editor api"
 ---
 

apps/docs/advanced/supereditor/overview.mdx

@@ -1,5 +1,6 @@
 ---
 title: SuperEditor API
+hidden: true
 sidebarTitle: Overview
 keywords: "supereditor class, prosemirror docx, tiptap alternative, editor commands, document manipulation api"
 ---

apps/docs/docs.json

@@ -232,22 +232,6 @@
               }
             ]
           },
-          {
-            "group": "Advanced",
-            "pages": [
-              {
-                "group": "SuperEditor",
-                "pages": [
-                  "advanced/supereditor/overview",
-                  "advanced/supereditor/configuration",
-                  "advanced/supereditor/methods",
-                  "advanced/supereditor/events"
-                ]
-              },
-              "advanced/headless-toolbar",
-              "advanced/headless-toolbar-examples"
-            ]
-          },
           {
             "group": "Resources",
             "pages": [