`@apphosting/build` is missing `yaml` in its declared dependencies

[baraknaveh]

@apphosting/build@0.1.7 requires yaml at runtime (dist/index.js:13) but does not list it in its dependencies. This works under npm's flat node_modules layout (where yaml is hoisted from a sibling package), but fails under pnpm's strict isolation:

Error: Cannot find module 'yaml'
Require stack:
- .../node_modules/@apphosting/build/dist/index.js
- .../node_modules/firebase-tools/lib/apphosting/localbuilds.js
- .../node_modules/firebase-tools/lib/deploy/apphosting/prepare.js
  ...

Steps to reproduce:

1. Use pnpm with hoist: false in a workspace
2. Install firebase-tools@15.13.0
3. Run firebase deploy --only functions

Expected: Deploy succeeds — @apphosting/build resolves yaml from its own dependencies.

Actual: Cannot find module 'yaml' error.

Workaround: Add a packageExtensions entry in pnpm-workspace.yaml:

packageExtensions:
  "@apphosting/build@0":
    dependencies:
      yaml: "*"

Fix: Add yaml to dependencies in packages/@apphosting/build/package.json.