Evaluate reusable workflows (`workflow_call`)

[Co-Messi]

Body:

workflow_call workflows are currently classified but not evaluated. A calling workflow that uses: a reusable workflow should have that call expanded so its jobs appear in the verdict tree.

Scope:

• Detect jobs.<id>.uses: pointing at a local reusable workflow.
• Parse the called workflow and evaluate its jobs in the caller's context, passing with: inputs through.
• Represent the nesting in both the CLI tree and the report model.

Start with local reusable workflows (same repo, ./.github/workflows/x.yml); remote owner/repo/.github/workflows/x.yml@ref can be a follow-up (it needs network or a checkout, which conflicts with the zero-network guarantee — discuss in the issue first).

---