style(simulation): gate bounce — box GenCompletion::BodyAnalyzed state; clippy/fmt sweeps

BodyWorldState grew past clippy's large-enum-variant threshold when it
began retaining Layer1Output (T-1170 Ruling 4b) — boxed, with the two
insert sites deref'd; manual_contains x2 (drainage tests),
cloned_ref_to_slice_refs x3 (river_course tests), fmt wraps.
gen_queue 18/18; clippy -D warnings clean; fmt --check clean.

Tickets: T-1170

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/src/atlas/gen_queue.rs

@@ -272,7 +272,10 @@ pub enum GenCompletion {
     BodyAnalyzed {
         body_id: String,
         /// The computed world state, ready for `BodyWorldStateCache::insert`.
-        state: BodyWorldState,
+        /// Boxed: `BodyWorldState` grew past clippy's large-enum-variant
+        /// threshold when it began retaining `Layer1Output` (T-1170 Ruling 4b)
+        /// — the box keeps the enum small while the state moves by pointer.
+        state: Box<BodyWorldState>,
     },
     SkeletonGenerated {
         city_id: u64,
@@ -726,7 +729,7 @@ fn run_work_item(
                 );
                 GenCompletion::BodyAnalyzed {
                     body_id: body_id.clone(),
-                    state: snapshot.into_body_world_state(),
+                    state: Box::new(snapshot.into_body_world_state()),
                 }
             }
             Err(e) => GenCompletion::Failed {