feat(spec-api): typed surface for spec authors

Thin wrappers over a globalThis.__uatu__ runtime that the verifier
provides as host bindings. Spec authors get IntelliSense for
extract/always/Tap/InputText/actions/weighted/taps/swipes, but the
bundle stays small because runtime logic lives in goja.

pkg/spec-api/src/extract.ts

@@ -0,0 +1,5 @@
+import type { Extracted, State } from "./types.ts";
+
+export function extract<T>(getter: (state: State) => T): Extracted<T> {
+  return globalThis.__uatu__.extract(getter);
+}