Add M3 error pages and the Markdown mail theme

Error pages for 401 to 503 in an error-view root appended to view.paths,
with an inline fallback when the Vite build is missing, and a mail theme
rendered from the application's scheme JSON, with opt-in header and
message components. Completes Phase 9.

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

src/Support/Scheme.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace NoNameWeb\LivewireMaterial\Support;
+
+/**
+ * The colour scheme as data, for the places CSS custom properties cannot reach: a mail client
+ * resolves none, and an error page whose build is missing has no stylesheet to declare them.
+ *
+ * The data is the JSON `php artisan material:scheme` writes beside the stylesheet
+ * (`livewire-material.scheme`, resources/css/material-scheme.json by default). Without that
+ * file — or with one that is not a scheme — the package's own default applies, the same one
+ * tokens/scheme.css carries. A role the application's file lacks (a scheme generated before
+ * the role existed) is taken from the default, and a value that is not a #rrggbb hex is
+ * refused, so nothing but a colour ever reaches a stylesheet.
+ *
+ * Read on every call and never kept: a regenerated scheme applies at once, and a long-running
+ * worker holds nothing.
+ */
+class Scheme
+{
+    /**
+     * @return array{light: array<string, string>, dark: array<string, string>}
+     */
+    public static function load(?string $path = null): array
+    {
+        $default = static::read(dirname(__DIR__, 2).'/resources/css/tokens/scheme.json');
+        $scheme = static::read($path ?? (string) config('livewire-material.scheme'));
+
+        return [
+            'light' => [...$default['light'], ...$scheme['light']],
+            'dark' => [...$default['dark'], ...$scheme['dark']],
+        ];
+    }
+
+    /**
+     * The light roles: what a mail wears.
+     *
+     * @return array<string, string>
+     */
+    public static function light(?string $path = null): array
+    {
+        return static::load($path)['light'];
+    }
+
+    /**
+     * @return array{light: array<string, string>, dark: array<string, string>}
+     */
+    protected static function read(string $path): array
+    {
+        $data = is_file($path) ? json_decode((string) file_get_contents($path), true) : null;
+
+        return [
+            'light' => static::roles($data['light'] ?? null),
+            'dark' => static::roles($data['dark'] ?? null),
+        ];
+    }
+
+    /**
+     * @return array<string, string>
+     */
+    protected static function roles(mixed $roles): array
+    {
+        if (! is_array($roles)) {
+            return [];
+        }
+
+        return array_filter(
+            $roles,
+            fn (mixed $hex, mixed $role): bool => is_string($role)
+                && preg_match('/^[a-z-]+$/', $role) === 1
+                && is_string($hex)
+                && preg_match('/^#[0-9a-fA-F]{6}$/', $hex) === 1,
+            ARRAY_FILTER_USE_BOTH,
+        );
+    }
+}