feat: implement dynamic rule discovery and incremental level filtering

src/Rules/AriaFocusable.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace YakNet\AccessibilityConsole\Rules;
+
+use DOMElement;
+use YakNet\AccessibilityConsole\Core\Severity;
+use YakNet\AccessibilityConsole\Core\Violation;
+use YakNet\AccessibilityConsole\Core\WCAGStandard;
+
+class AriaFocusable extends AbstractRule
+{
+    /** @var array<int, string> */
+    private static array $interactiveRoles = [
+        'button', 'link', 'checkbox', 'menuitem', 'radio', 'textbox',
+        'searchbox', 'slider', 'spinbutton', 'switch', 'tab'
+    ];
+
+    /** @var array<int, string> */
+    private static array $nativeFocusable = [
+        'a', 'button', 'input', 'select', 'textarea', 'iframe'
+    ];
+
+    public function getId(): string { return 'WCAG_2_1_1_ARIA_FOCUSABLE'; }
+    public function getDescription(): string { return 'Elements with interactive ARIA roles must be focusable (e.g. have a tabindex attribute).'; }
+    public function getStandard(): WCAGStandard { return WCAGStandard::A; }
+    public function getSeverity(): Severity { return Severity::WARNING; }
+    public function getLevel(): int { return 3; }
+
+    public function check(DOMElement $element): ?Violation
+    {
+        if (!$element->hasAttribute('role')) {
+            return null;
+        }
+
+        $role = strtolower(trim($element->getAttribute('role')));
+        if (!in_array($role, self::$interactiveRoles, true)) {
+            return null;
+        }
+
+        $tagName = strtolower($element->tagName);
+        if (in_array($tagName, self::$nativeFocusable, true)) {
+            return null;
+        }
+
+        if (!$element->hasAttribute('tabindex')) {
+            return $this->createViolation(
+                $element,
+                $this->getDescription(),
+                'Add tabindex="0" to make the element focusable via keyboard navigation.'
+            );
+        }
+
+        return null;
+    }
+}