Render badge slots as HTML and add neutral and plain badge colours

The slot was cast to a string and escaped, so an icon beside a badge's
word showed as literal markup. It renders as HTML now; `value` stays
escaped, and a slot holding only whitespace or comments is still a dot
(hasActualContent rather than isNotEmpty).

`color="neutral"` draws neutral ink on every variant: a dot or count in
on-surface-variant with surface text (the ink the outline badge already
writes in), a tonal label in surface-container-high with
on-surface-variant text, and an outline in outline-variant.

`color="plain"` emits no background, text or border colour in any
variant, keeping shape, size and type, so an application's own colour
classes paint it without racing the badge's.

Every existing colour renders the same classes as before, and an unknown
colour still falls back to error.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RHoXZSHc8gGpZjFmA5fPc2

resources/views/showcase/sections/communication.blade.php

@@ -8,6 +8,11 @@
             <x-badge value="Active" color="success" tonal />
             <x-badge value="Password" color="info" tonal />
             <x-badge value="Pro" outline />
+            <x-badge value="Draft" color="neutral" tonal />
+            <x-badge value="Archived" color="neutral" outline />
+            <span class="relative inline-flex"><x-icon name="chat" /><x-badge value="2" color="neutral" floating /></span>
+            <x-badge tonal color="tertiary"><x-icon name="bolt" filled class="size-3" /> Pro</x-badge>
+            <x-badge value="Beta" tonal color="plain" class="bg-primary-fixed text-on-primary-fixed" />
             BLADE,
         'Snackbars' => <<<'BLADE'
             <div x-data class="flex flex-wrap items-center gap-4">