fix(neuron): correct nccl_state path on WorkerPool.leader_comm (#17 S2)

`super::nccl_state` from tp/mod.rs resolves to `crate::harness::nccl_state`
(nonexistent); the module is the child `nccl_state` (cf. the existing
`nccl_state::generate_comm_id_hex` call). The field is cuda-gated so the
non-cuda build couldn't catch it; the branch CUDA type-check flaked on the
runner before compiling. Self-audited fix.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/neuron/src/harness/tp/mod.rs

@@ -253,7 +253,7 @@ pub struct WorkerPool {
     /// recovery's `unload` doesn't itself hang (#17 Stage 2). `None` if
     /// init couldn't cache it; the watchdog then logs that it can't abort.
     #[cfg(feature = "cuda")]
-    leader_comm: Option<super::nccl_state::SendComm>,
+    leader_comm: Option<nccl_state::SendComm>,
 }
 
 /// Per-step deadline for a TP forward (#17 Stage 2). A healthy decode