Give the frontend's check scripts something that runs them

Eight `*.check.ts` scripts existed and nothing ran any of them, so a
helper's arithmetic was only checked by hand. `make test-checks` runs
every one and `make test` now includes it — they need no stack, so they
sit between the backend suite and Playwright.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KYM38KSb4V4v2T71eifnZv

Makefile

@@ -3,7 +3,7 @@
 # The workspace root delegates to these (see ../Makefile).
 
 .PHONY: dev-utils dev dev-local dev-lan rebuild-frontend up down update install dev-backend dev-frontend \
-        generate-client sync-example test test-backend test-frontend soak bench-startup lint lint-backend \
+        generate-client sync-example test test-backend test-checks test-frontend soak bench-startup lint lint-backend \
         lint-frontend format-frontend umami build docs docs-serve clean help
 
 COMPOSE_ROOT := $(CURDIR)
@@ -143,7 +143,13 @@ sync-example:  ## Upload `examples/myresearch` the way a data scientist would
 
 # ── Testing ───────────────────────────────────────────────────────
 
-test: test-backend test-frontend  ## Run all tests (backend + frontend)
+test: test-backend test-checks test-frontend  ## Run all tests (backend + checks + frontend)
+
+# The frontend has no unit-test runner, so a pure helper is checked by a
+# `*.check.ts` script of plain `node:assert` that runs itself and needs no
+# stack. This is the target that runs every one of them.
+test-checks:  ## Run the frontend's *.check.ts scripts
+	cd frontend && bun run check
 
 test-backend:  ## Run backend tests (pytest + coverage)
 	# Its own SQLite file in a temp directory (tests/__init__.py), so this needs