feat(messaging-ui): rendered Messenger components — the drop-in UI

Turns the SDK from hooks-only into a real UI SDK: <Messenger> (conversation
list + open thread + composer), plus <ConversationList> and <Thread>, all
driven by the existing useConversations/useMessages hooks over the injected
adapter — zero transport imports (boundary intact).

- themeable via --miu-* CSS variables; default theme ships as ./styles.css
- optimistic send, typing indicator, seen ticks, reactions display, unread badges
- render smoke tests (jsdom + MockAdapter): mounts, auto-selects first thread,
  sends a message, switches threads (3 tests) — 48 total green
- tsup: css bundled to dist/styles.css; dts scoped to TS entries

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-messaging-ui/tsup.config.ts

@@ -6,9 +6,10 @@ export default defineConfig({
   // entry, never reachable from `index`, because it imports vitest, and bundling
   // that into the main barrel would drag a test runner into every consumer's
   // production build.
-  entry: ['src/index.ts', 'src/adapters/mock.ts', 'src/adapters/kernel-client.ts', 'src/conformance.ts'],
+  entry: ['src/index.ts', 'src/adapters/mock.ts', 'src/adapters/kernel-client.ts', 'src/conformance.ts', 'src/styles.css'],
   format: ['esm'],
-  dts: true,
+  // Types only for the TS entries — styles.css has no .d.ts (and tsc chokes on a .css root file).
+  dts: { entry: ['src/index.ts', 'src/adapters/mock.ts', 'src/adapters/kernel-client.ts', 'src/conformance.ts'] },
   clean: true,
   external: ['react', 'react-dom', 'vitest', '@insignia/iios-kernel-client'],
 });