feat: implement dynamic rule discovery and incremental level filtering

src/Rules/EmptyHeading.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace YakNet\AccessibilityConsole\Rules;
+
+use DOMElement;
+use YakNet\AccessibilityConsole\Core\Severity;
+use YakNet\AccessibilityConsole\Core\Violation;
+use YakNet\AccessibilityConsole\Core\WCAGStandard;
+
+class EmptyHeading extends AbstractRule
+{
+    public function getId(): string { return 'WCAG_1_3_1_EMPTY_HEADING'; }
+    public function getDescription(): string { return 'Heading elements (h1-h6) must have discernible text content.'; }
+    public function getStandard(): WCAGStandard { return WCAGStandard::A; }
+    public function getSeverity(): Severity { return Severity::ERROR; }
+    public function getLevel(): int { return 2; }
+
+    public function check(DOMElement $element): ?Violation
+    {
+        if (!preg_match('/^h([1-6])$/i', $element->tagName)) {
+            return null;
+        }
+
+        $text = trim($element->textContent);
+        if ($text === '' && !$element->hasAttribute('aria-label') && !$element->hasAttribute('title')) {
+            return $this->createViolation(
+                $element,
+                $this->getDescription(),
+                'Add descriptive text or an aria-label to the heading element.'
+            );
+        }
+
+        return null;
+    }
+}