fix(syncedinstance): Prevent same-instance syncs and sanitize post update payloads; update tests and docs

ts/classes.syncedinstance.ts

@@ -50,6 +50,20 @@ export class SyncedInstance {
   private syncHistory: ISyncReport[];
 
   constructor(sourceGhost: Ghost, targetGhosts: Ghost[]) {
+    // Validate that no target instance is the same as the source instance
+    const sourceUrl = sourceGhost.options.baseUrl.replace(/\/$/, '').toLowerCase();
+
+    for (const targetGhost of targetGhosts) {
+      const targetUrl = targetGhost.options.baseUrl.replace(/\/$/, '').toLowerCase();
+
+      if (sourceUrl === targetUrl) {
+        throw new Error(
+          `Cannot sync to the same instance. Source and target both point to: ${sourceUrl}. ` +
+          `This would create a circular sync and cause excessive API calls.`
+        );
+      }
+    }
+
     this.sourceGhost = sourceGhost;
     this.targetGhosts = targetGhosts;
     this.syncMappings = new Map();
@@ -125,6 +139,7 @@ export class SyncedInstance {
             if (!optionsArg?.dryRun) {
               await targetTag.update({
                 name: sourceTag.name,
+                slug: sourceTag.slug,
                 description: sourceTag.description,
                 feature_image: sourceTag.feature_image,
                 visibility: sourceTag.visibility,