Give each canonical layout a page of its own in the Layout section

Plan step 38: the Layout section's Overview keeps its breakpoint
table and live "This window" readout (now a shared
<x-showcase::breakpoint-readout> partial, and the five breakpoint
cards a real range-queried data-md-showcase-breakpoint-card instead
of Tailwind's max-medium:/medium:max-expanded: variants), but the
three canonical layouts move off it onto a page of their own:
/material/layout/{list-detail,supporting-pane,feed}
(ShowcaseController::layout(), routes/showcase.php), each built on
the real component, sharing one <x-section-nav> Sections::
layoutPages() feeds. The search index gains an entry per page with
its own URL, and the component-homes scan now also reads the three
pages' own source so <x-list-detail>, <x-supporting-pane> and
<x-feed> keep a home.

The whole section moves onto the layout components and md-* classes:
no bespoke Tailwind grid or table styling remains.

LayoutTest's browser test now visits the three dedicated pages
instead of one shared /material/layout; a new Feature test asserts
each page renders and is linked from the Layout section.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

src/Http/Controllers/ShowcaseController.php

@@ -24,6 +24,19 @@ class ShowcaseController
         ]);
     }
 
+    /**
+     * One of the Layout section's own pages (plan step 38): a canonical layout on a page of its
+     * own, sharing the Layout section's rail entry and title.
+     */
+    public function layout(string $page): View
+    {
+        return view('livewire-material::showcase.layout.'.$page, [
+            'sections' => Sections::all(),
+            'section' => 'layout',
+            'title' => Sections::layoutPages()[$page]['title'].' · Layout',
+        ]);
+    }
+
     /**
      * The search's index, fetched when the search is first focused rather than written into every page.
      */