chore(cli): add basic "Hello, world!" output to CLI entry point

Introduced a `main` function that logs "Hello, world!" to the console, providing a basic implementation for the CLI entry point. This serves as an initial scaffold for later functional enhancements and ensures the CLI produces visible output when executed.

Author: thevuong

packages/cli/src/index.ts

@@ -1 +1,7 @@
 #!/usr/bin/env node
+
+function main(): void {
+  console.log("Hello, world!");
+}
+
+main();