chore: add typescript for type-check script (#12)

The `type-check` script expectes `tsc` to exist, but we don't actually
install typescript yet as a direct dependency.

This adds typescript as a dev dependency so the type-check script works
again.

CI somehow does discover `tsc` before this change, but local installs do
not.

Author: 43081j

package.json

@@ -30,6 +30,7 @@
     "prettier": "^3.4.2",
     "tsup": "^8.3.6",
     "tsx": "^4.19.1",
+    "typescript": "^5.7.3",
     "vitest": "^2.1.3"
   },
   "dependencies": {