agent: fix CI — drop tracker tag in checks.nix comment, regenerate npmDepsHash

- nix/checks.nix: 'hyperhive#3685' in a source comment trips the
  tracker-tag lint (prose-only, per hive-rules.md) — argus caught it on
  review. Reworded without the ref.
- frontend/npm-deps-hash: the earlier scaffold commit
  (be18f460) added preact/typescript to agent/package.json, which
  regenerated package-lock.json but never re-derived this hash in
  lockstep — nix flake check's frontend derivation was failing on a
  hash mismatch. Regenerated via
  'nix run nixpkgs#prefetch-npm-deps -- frontend/package-lock.json'.

frontend/npm-deps-hash

@@ -1 +1 @@
-sha256-8mYI9b1nuQ8YNFkW/ezJwO5Qw6NJTDG+kspYozs/5cI=
+sha256-9sh4G6A00NNi5YKaMQ1v0vZQj+gmGxYPhYZhlqweApM=

nix/checks.nix

@@ -176,9 +176,9 @@ in
   };
 
   # Same rationale + shape as `swarm-ui-typecheck` above, for the `agent`
-  # package now that its Preact rewrite (hyperhive#3685) has grown enough
-  # real `.tsx`/`.ts` for a type error to matter — argus flagged the same
-  # gap on that PR's review.
+  # package now that its ongoing Preact rewrite has grown enough real
+  # `.tsx`/`.ts` for a type error to matter — argus flagged the same gap
+  # on that PR's review.
   agent-typecheck = pkgs.buildNpmPackage {
     pname = "hyperhive-agent-typecheck";
     version = "0.0.0";