fix(simulation): lower storyteller activation_pass log to debug (#789)

The "no co-present NPC assigned to a Simmering triangle" branch fires
as WARN every few seconds during early gameplay when no NPC relationships
have escalated. This is normal state, not an error condition — downgrade
to debug so the warning channel reflects actual problems.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/storyteller/mod.rs

@@ -535,7 +535,7 @@ pub fn activation_pass(
     }
 
     if candidates.is_empty() {
-        tracing::warn!(
+        tracing::debug!(
             "activation_pass: no co-present NPC is assigned to a Simmering triangle at tick {} — holding",
             time.tick
         );