Add yaml dependency to apphosting build package

[kingmarh-hash]

Summary

• declare yaml as a runtime dependency of @apphosting/build
• update the root lockfile workspace entry for packages/@apphosting/build

Why

packages/@apphosting/build/src/index.ts imports parse from yaml, but the package did not declare yaml in its dependencies. npm flat installs can hide this through sibling dependencies, but strict package layouts such as pnpm isolated/no-hoist can fail when Firebase CLI loads App Hosting local build code.

Fixes #556.

Verification

• Reproduced the published failure with firebase-tools@15.13.0 in a temporary pnpm project using node-linker=isolated and hoist=false: loading firebase-tools/lib/apphosting/localbuilds.js failed with MODULE_NOT_FOUND Cannot find module 'yaml'.
• npm ci --ignore-scripts --no-audit --no-fund
• npm --workspace @apphosting/common run build
• npm --workspace @apphosting/build run build
• git diff --check

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gemini-code-assist]

Code Review

This pull request adds the yaml dependency (version ^2.3.4) to the @apphosting/build package and updates the package-lock.json file. There are no review comments, and I have no feedback to provide.