Count a text field's characters against its maximum

M3 lists "supporting text + character counter" as a configuration of both
text-field variants; nothing in the package drew one (plan step 24, audit
docs/audits/m3-alignment/inputs.md § Missing). `counter` on `<x-input>` and
`<x-textarea>` now puts `n/max` at the end of the supporting-text row, counted
from the control on every input, in the error colour past the maximum, and said
as M3's own "Character count, 5/20" from a polite region once typing settles.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

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

@@ -41,6 +41,16 @@
                 </div>
             </div>
             BLADE,
+        'Character counter' => <<<'BLADE'
+            <div class="grid w-full gap-6 medium:grid-cols-2">
+                <div class="grid content-start gap-4">
+                    <x-input label="Share name" maxlength="40" counter hint="Recipients see this name" />
+                    <x-input variant="filled" label="Subject" maxlength="60" counter />
+                </div>
+
+                <x-textarea label="Message for recipients" maxlength="180" counter rows="3" hint="Sent with the link" />
+            </div>
+            BLADE,
         'Textarea and select' => <<<'BLADE'
             <div class="grid w-full gap-6 medium:grid-cols-2">
                 <div class="grid content-start gap-4">