feat: add app and database modules

app/Exceptions/SystemConfigException.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Exceptions;
+
+use RuntimeException;
+
+class SystemConfigException extends RuntimeException
+{
+    public static function unknownKey(string $key): self
+    {
+        return new self("Unknown system setting key: {$key}");
+    }
+
+    public static function imageUploadFailed(string $key, string $reason): self
+    {
+        return new self("Failed to upload image for setting '{$key}': {$reason}");
+    }
+}