chore: scrub #NNN issue references from code comments and nix descriptions

Part of the docs-migration chore (issue #708). Remove GitHub issue
numbers from inline comments, option descriptions, and rustdoc —
these are contextless noise for anyone reading the code without
access to the original discussions. Replace with prose that captures
the same rationale directly.

No functional change. Build still clean (cargo check passes).

hive-c0re/src/server.rs

@@ -189,7 +189,7 @@ async fn dispatch(req: &HostRequest, coord: Arc<Coordinator>) -> HostResponse {
             HostRequest::SetParent { child, new_parent } => {
                 tracing::info!(%child, ?new_parent, "set_parent");
                 // `reparent_with_notify` wraps `topology::set_parent`
-                // with the three notification messages (#743) + the
+                // with the three notification messages + the
                 // ContainerView rescan. Idempotent same-parent calls
                 // skip both the messages and the disk write per the
                 // topology fast-path.