feat(sdk): P2.5 @insignia/iios-kernel-client — REST + socket facade

MessageSocket (open/send/read/typing via emitWithAck, reconnect re-opens thread,
no socket.io types leak) + RestClient (ingest/getThreadMessages/sendMessage).
tsup ESM+dts. Facade unit test with injectable fake socket (3 tests).

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

packages/iios-kernel-client/tsup.config.ts

@@ -0,0 +1,9 @@
+import { defineConfig } from 'tsup';
+
+export default defineConfig({
+  entry: ['src/index.ts'],
+  format: ['esm'],
+  dts: true,
+  clean: true,
+  external: ['react'],
+});