Argus flagged on this PR's review that esbuild only strips TS types
without checking them, so a real type error would build clean and
pass every other check. Mara asked for it to be wired in on the same
PR.
Adds checks.swarm-ui-typecheck: a separate buildNpmPackage derivation
(not folded into swarm-ui.nix itself, which doesn't need typescript in
node_modules for its actual esbuild-only build) running
'npm run typecheck --workspace=packages/swarm-ui', same shared
npmDepsHash as frontend/swarm-ui.
Verified: nix build .#checks.x86_64-linux.swarm-ui-typecheck succeeds;
nix fmt clean; scripts/check-issue-refs.sh clean.
b10cce8045