test: add smoke tests for all package manager variants (yarn, pnpm, bun)

[ulises-jeremias]

Description

CI only tests npm. CLI supports --use-yarn, --use-pnpm, --use-bun but these are untested.

Files to modify

• .github/workflows/test.yml — add matrix jobs per package manager
• .github/workflows/smoke-distribution.yml — add PM variants

Verification

• CI passes for yarn, pnpm, bun scaffolding

[ulises-jeremias]

Note for contributors: this issue is a bit larger than a typical good first issue (design/integration surface). Removing the good first issue label so newcomers can focus on smaller scoped tickets. Still very welcome if you want to take it on — ping a maintainer first.