feat: export messaging-ui public API and enforce transport boundary

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-messaging-ui/src/index.ts

@@ -1 +1,24 @@
-export {};
+// Public API. Components land in Plan 2; adapters/kernel in Plan 3.
+//
+// `runAdapterConformance` is deliberately NOT exported here — it imports vitest and
+// ships from the './conformance' subpath so consumers never pull a test runner into
+// their production bundle.
+export { MessagingProvider, useAdapter } from './provider';
+export { useConversations } from './hooks/use-conversations';
+export { useMessages } from './hooks/use-messages';
+export { isOwnMessage } from './types';
+
+export type { MessagingAdapter } from './adapter';
+export type { ConversationsState } from './hooks/use-conversations';
+export type { MessagesState, UiMessage } from './hooks/use-messages';
+export type {
+  Attachment,
+  Conversation,
+  Membership,
+  Message,
+  MessageEvent,
+  Person,
+  Reaction,
+  SendOpts,
+  Unsubscribe,
+} from './types';