Add bunext playground for local component development

Runs at http://localhost:7010 via bun run dev. The playground imports the library from src through a committed symlink and tsconfig path alias, so component edits hot-reload without a build step. It has its own install root and is excluded from the published package.

dev/bunext.config.ts

@@ -0,0 +1,7 @@
+import type { BunextConfig } from "@moduletrace/bunext/types";
+
+const config: BunextConfig = {
+    port: 7010,
+};
+
+export default config;