Fix len_zero clippy warning in tests

Replace len() > 0 with !is_empty() for clearer intent

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: platinummonkey

tests/e2e_organizer_tests.rs

@@ -394,7 +394,7 @@ async fn test_organizer_add_label_to_talk() {
         .await
         .expect("Failed to find talk labels");
 
-    assert!(labels.len() > 0, "Should have at least one label");
+    assert!(!labels.is_empty(), "Should have at least one label");
 
     ctx.cleanup().await;
     cleanup_database()