Render a `needs:` DAG as an ASCII graph

[Co-Messi]

Body:

When a job is skipped because a dependency was skipped, it would help to see the needs: graph. Add an optional ASCII rendering of the job DAG to the CLI output (perhaps behind a --graph flag) so the propagation is visible.

Scope:

• Build a small ASCII/box-drawing renderer for the job dependency graph.
• Annotate each node with its verdict (fires / skipped / unknown).
• Keep it readable for the common small-DAG case; large graphs can degrade gracefully.

The core already exposes needs on each JobVerdict, so this is a rendering-only task in src/cli/.

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