bug: GitHub Integration uses Node 20 for install phase, ignoring runtime config

[isshaddad]

Provide environment information

N/A - This is a build server issue, not a local environment issue

Describe the bug

When using GitHub Integration, the build server runs dependency installation with Node 20.19.6, even when runtime: 'node-22' is set in trigger.config.ts. The runtime setting is only respected for the Docker image build, not for the install phase.

This causes failures when projects have strict Node version requirements in their package.json (e.g., engines.node: "21.1.0"), as the install phase fails with engine compatibility errors.

Expected behavior: The build server should read trigger.config.ts before running installs and use the Node version specified in the runtime field (or at least allow specifying a Node version for the install phase separately).

Reproduction repo

n/a

To reproduce

1. Set up a project with runtime: 'node-22' in trigger.config.ts
2. Set engines.node: "21.1.0" in package.json
3. Connect GitHub Integration
4. Push to a tracked branch
5. Observe build failure during install phase with Node version mismatch

Additional information

This affects the build server infrastructure (separate from the CLI codebase). The runtime config is correctly respected for the Docker image selection, but not for the install phase that happens before the Docker build.