package root export points to missing dist/src/index.js

## Summary

`bedrock-agentcore@0.2.4` publishes the package root at `dist/src/index.js`, but the npm package does not include `dist/src/index.js` or `dist/src/index.d.ts`.

Other subpath entrypoints such as `./runtime` and `./identity` are present, so this looks like a missing root build artifact or stale root export.

## Reproduction

```sh
tmp="$(mktemp -d)"
cd "$tmp"
npm init -y >/dev/null
npm install --ignore-scripts bedrock-agentcore@0.2.4

node - <<'NODE'
const fs = require('node:fs');
const path = require('node:path');
const root = path.join(process.cwd(), 'node_modules/bedrock-agentcore');
const pkg = JSON.parse(fs.readFileSync(path.join(root, 'package.json'), 'utf8'));

console.log({ main: pkg.main, rootExport: pkg.exports['.'] });
for (const file of [
'dist/src/index.js',
'dist/src/index.d.ts',
'dist/src/runtime/index.js',
'dist/src/identity/index.js',
]) {
console.log(file, fs.existsSync(path.join(root, file)));
}
NODE

node -e "import('bedrock-agentcore')"
```

## Actual behavior

Root import fails with `ERR_MODULE_NOT_FOUND` because `dist/src/index.js` is absent.

## Expected behavior

The package root should import successfully, or the root export and `main` should point to an included file.

Environment used to reproduce: macOS, Node v24.10.0, npm 11.6.0.

Start by inspecting package.json and the published package contents referenced in the reproduction, especially the root export, main field, and dist/src/index.js and dist/src/index.d.ts paths. Run the provided npm install and node import checks; done means the package root imports successfully and its declared root entry files are included or point to included files.

Written by the indexing model from the issue text.