fix: pass project and production stack in sample workflows

[simple-agent-manager]

Summary

• pass the generated repo name as the Defang project in sample template workflows
• default sample template deploys to the production stack instead of an empty stack input
• add a workflow generator regression test so the project/stack inputs stay in the canonical template

Why

Portal PR DefangLabs/portal#901 creates the BYOC Fabric stack before cloning a sample, but the generated sample workflow still invoked defang-github-action without a project and with an empty stack on push. For samples like sveltekit, the CLI derived the Compose project name from compose.yaml and then fell back to playground when it could not load the repo-named Fabric stack.

With this workflow change, the initial template-generated push uses project=${{ github.event.repository.name }} and stack=production, matching the stack Portal creates before cloning.

Test

• npm test (projects/samples/scripts)