feat: initialize drainage network frontend

features/agent/ui-envelope/index.ts

@@ -0,0 +1,8 @@
+export type { UIEnvelope, UIEnvelopePayload, UIRegistry, UISurface } from "./types";
+export { toTrustedMapAction, type TrustedMapAction } from "./map-actions";
+export {
+  isUiEnvelopeAllowed,
+  parseUiEnvelope,
+  parseUiEnvelopePayload,
+  parseUiRegistry
+} from "./validator";