Remove material.css, the 1.x single-import shortcut

Plan step 37: an application on 1.x-style imports now imports
foundation.css before @import 'tailwindcss' and tailwind.css after it,
the way foundation.css's own header has described since Phase F
started — material.css only ever saved writing those two lines.
Updates every place that named it: tailwind.css's and
foundation/hidden.css's and tokens/utilities.css's header comments,
the development skill's install snippet and Tokens section, README.md's
install snippet, and a new line in UPGRADE.md's migration notes.

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

UPGRADE.md

@@ -124,7 +124,14 @@ over a colour, use the role directly.
   `heights` or `snap` is set; without stops it behaves as before.
 - A chip set with `scroll` shows a scroll button over each overflowing edge on fine pointers.
 
-### 6. New in 2.0.0
+### 6. `material.css` is gone
+
+The 1.x single-import shortcut no longer exists. An application still building Tailwind imports
+`foundation.css`, then `tailwindcss`, then `tailwind.css` in its place (see Installation in
+`README.md`); one that has already left Tailwind imports `foundation.css` plus the stylesheet of
+each component its views render, or `resources/css/all.css` for everything at once.
+
+### 7. New in 2.0.0
 
 Nothing to migrate, but worth knowing: submenus (`<x-menu-item submenu>`), a filtering menu
 (`<x-menu filter>`), a menu that opens as a bottom sheet on compact windows
@@ -141,14 +148,14 @@ side sheet (`<x-drawer standard>`), bottom sheet preset heights, the multi-aspec
 compact windows, search's icon entry point and suggestions (`trigger="icon"`, `suggestions` slot),
 the contrast toggle (`<x-theme-toggle mode="contrast">`) and the Standard motion scheme.
 
-### 7. Tests and guards
+### 8. Tests and guards
 
 Add `DesignGuard`'s new checks to the application's design test (`forbidOpacityInk()` and
 `forbidAbsolutes()` are opt-in). Browser tests that assert widths switch at 640/1024/1280 now
 switch at 600/840/1200; tests that read `role="alert"` on an alert, `aria-pressed` on the time
 picker's period buttons or `data-theme-option` need the new hooks above.
 
-### 8. For AI agents
+### 9. For AI agents
 
 `php artisan boost:update --discover` picks up the new `material-3` guideline and the
 `material-3-design` skill, which state M3's rules and tables beside the library's utilities.