fix(iris-chat): skip importing empty sessions from Artemis

Empty sessions (0 messages) created but never used on Artemis were
imported and shown in the session list, then vanished on click when
cleanupEmptySessions ran. Filter them out during import instead.

Author: Predixx

extension/src/extension/services/iris/sessionSyncUtils.ts

@@ -59,6 +59,12 @@ export function importSessionsToStore(
 
     for (const session of sessions) {
         const messageCount = session.messages?.length || 0;
+
+        // Skip empty sessions — they were created but never used
+        if (messageCount === 0) {
+            continue;
+        }
+
         const createdAt = session.creationDate ? new Date(session.creationDate).getTime() : Date.now();
 
         // Extract preview from first user message using shared content extractor