chore: drop src from publish (#474)

Publish shouldn't need the source files published along with the
distributable bin.

`src` is being shipped to the registry rn:
https://www.npmjs.com/package/@openai/codex?activeTab=code

You can verify that the src is not needed by packing the project
manually after removing src from the files:

```sh
# from the codex-cli dir
rm -rf dist # just for hygiene
pnpm run build
pnpm pack

mkdir /tmp/codex-tar-test
mv openai-codex-0.1.2504181820.tgz /tmp/codex-tar-test
cd /tmp/codex-tar-test

pnpm init
pnpm add ./openai-codex-0.1.2504181820.tgz /tmp/codex-tar-test
pnpm exec codex --full-auto "run a bash -c command to echo hello world"
```

The cli is operational

> noticed this when checking the screenshot included in
https://github.com/openai/codex/pull/461