Put the showcase in the app shell, with a page per section

The showcase is now an overview and one page per section behind a
grouped navigation rail, moved between with wire:navigate, instead of
one long page under a scrolling top bar. The switch exposed a WebKit
bug in the menu: inside a focusable region, WebKit moves focus out of
the closing popover before its toggle event, so Escape no longer
returned focus to the trigger. The menu now reads it on beforetoggle.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9NnLxnPp8vaaurb3Z1MFy

docs/plans/livewire-material.md

@@ -589,12 +589,17 @@ pages and the mail theme by an agent in its own worktree. What changed from the
   `__DIR__.'/../resources/views/components'`: Blade names the view namespace after its hash, and
   compiled views keep that name.
 - **A test checks that every component appears in the showcase.**
+- **The showcase is the package's own app shell**: an overview at `/material` and a page per section
+  (`/material/{section}`, `Showcase\Sections`), grouped in the navigation rail, moved between with
+  wire:navigate. It turned up a WebKit bug in `<x-menu>`: inside a focusable region (the shell's
+  `<main tabindex="-1">`), WebKit hands focus back to that region as the popover closes, so the
+  menu now reads whether focus was inside on `beforetoggle` before returning it to the trigger.
 - **Verified in a fresh Laravel 13.31 application** (`composer create-project`, the package from a
   path repository, the README's CSS, JS and layout, `material:scheme "#4f46e5"`, `npm run build`):
   a Livewire page with an app bar, tabs, a card, a form with validation, a date picker, a dialog and
   a toast works without console errors; `/material` and the 404 page render in its scheme.
-- **Known gap:** `<x-datepicker>` has no clear button (`<x-timepicker clearable>` does); a date can be
-  emptied through its text input.
+- **`<x-datepicker clearable>`** empties a date, or both ends of a range, as `<x-timepicker clearable>`
+  does.
 
 ### Phase 11 — SealShare 2.0.0