fix(PathHelper): resolve PHPStan type errors from realpath() returning false

- Ensure realpath() result is validated before assignment
- Convert false return value to fallback dirname(__DIR__, 2)
- Guarantee $basePath is always a string, matching declared type
- Prevent passing string|false into join() which strictly requires string

Resolves PHPStan warnings:
• Static property $basePath does not accept string|false
• PathHelper::join() expects string, string|false given

Author: megyptm

src/Helpers/PathHelper.php

@@ -58,7 +58,13 @@ final class PathHelper
      */
     public static function base(?string $append = null): string
     {
-        self::$basePath ??= realpath(dirname(__DIR__, 2));
+        if (self::$basePath === null) {
+            $resolved = realpath(dirname(__DIR__, 2));
+            self::$basePath = is_string($resolved)
+                ? $resolved
+                : dirname(__DIR__, 2);
+        }
+
         return self::join(self::$basePath, $append);
     }