feat: add signed image repository sync

scripts/sync-image-repository.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace sammo;
+
+require dirname(__DIR__) . '/vendor/autoload.php';
+
+if (PHP_SAPI !== 'cli') {
+    fwrite(STDERR, "This command is CLI-only.\n");
+    exit(2);
+}
+
+$url = getenv('IMAGE_SYNC_URL') ?: 'https://sam-image.hided.net/v1/sync';
+$secretFile = getenv('IMAGE_SYNC_SECRET_FILE') ?: '/run/secrets/image_sync_core_secret';
+if (!is_file($secretFile)) {
+    fwrite(STDERR, "IMAGE_SYNC_SECRET_FILE is not readable.\n");
+    exit(2);
+}
+$secret = trim(file_get_contents($secretFile));
+$result = ImageSyncClient::sync($url, 'core', $secret, $argv[1] ?? null);
+fwrite(STDOUT, Json::encode($result) . PHP_EOL);