fix(examples): drop .js extension on macroRegistry import

Next/Turbopack's resolver in the docs build can't follow the explicit
.js extension to a sibling .ts file, which broke build:site. Other
examples in the repo import sibling files extensionless, so match that.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nperez0111

examples/06-custom-schema/09-macro-block/src/Macro.ts

@@ -1,6 +1,6 @@
 import { createBlockSpec, defaultProps } from "@blocknote/core";
 
-import { macroRegistry } from "./macroRegistry.js";
+import { macroRegistry } from "./macroRegistry";
 
 // The Macro block — built with the vanilla `createBlockSpec` API.
 //