fix(agent): update e2e_tests.rs call site for search_with_metrics's new vectors_flat parameter

Missed in the INT-16 flat-embedding-buffer commit — this integration
test call site lives under tests/, outside the src/ tree that was
grepped for callers.

crates/clawhdf5-agent/tests/e2e_tests.rs

@@ -1144,9 +1144,11 @@ fn test_strategy_reports_backend() {
     let tombstones = vec![0u8; n];
     let query = vectors[0].clone();
 
+    let flat: Vec<f32> = vectors.iter().flatten().copied().collect();
     let (_, metrics) = strategy::search_with_metrics(
         &query,
         &vectors,
+        &flat,
         &norms,
         &tombstones,
         5,