fix: pin tracing <0.1.41 to fix Send bound in tokio::spawn

tracing 0.1.41+ introduced PhantomNotSend in Span, making
#[instrument]-decorated async fns !Send. This breaks tokio::spawn
and JoinSet::spawn which require Send futures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ZhiXiao-Lin

Cargo.lock

@@ -39,7 +39,7 @@ anyhow = "1.0"
 thiserror = "1.0"
 
 # Logging (tracing only — no OTel)
-tracing = "0.1"
+tracing = ">=0.1, <0.1.41"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "json"] }
 
 # Async utilities