[TASK] Extract temp subdirectory path to constant

Extracts the temp subdirectory path to a public constant so tests
can reference it directly, ensuring they stay in sync with the
implementation.

Author: CybotTM

src/Graphs/Renderer/PlantumlRenderer.php

@@ -28,6 +28,8 @@
 
 final class PlantumlRenderer implements DiagramRenderer
 {
+    public const TEMP_SUBDIRECTORY = '/phpdocumentor';
+
     public function __construct(private readonly LoggerInterface $logger, private readonly string $plantUmlBinaryPath)
     {
     }
@@ -47,7 +49,7 @@ public function render(RenderContext $renderContext, string $diagram): string|nu
 @enduml
 PUML;
 
-        $tempDir = sys_get_temp_dir() . '/phpdocumentor';
+        $tempDir = sys_get_temp_dir() . self::TEMP_SUBDIRECTORY;
         if (!is_dir($tempDir)) {
             mkdir($tempDir, 0o777, true);
         }

tests/unit/Renderer/PlantumlRendererTest.php

@@ -28,7 +28,7 @@ final class PlantumlRendererTest extends TestCase
      */
     public function testRenderCreatesTempDirectoryWhenMissing(): void
     {
-        $tempDir = sys_get_temp_dir() . '/phpdocumentor';
+        $tempDir = sys_get_temp_dir() . PlantumlRenderer::TEMP_SUBDIRECTORY;
 
         // Remove the directory if it exists to test creation
         if (is_dir($tempDir)) {