feat(core): implement tenant-scoped system store manager

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

shared/lib/SystemStore/InvalidKeyException.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace KTXF\SystemStore;
+
+use InvalidArgumentException;
+
+/**
+ * Raised when a logical system-store key is not safely normalized.
+ */
+final class InvalidKeyException extends InvalidArgumentException
+{
+}