Render actionable guidance for a sandbox dependency-check failure.

The sandbox compile already runs Mix's authoritative dependency validation, so no speculative preflight is needed. Mutare.Sandbox.Command.Output classifies that captured output; this module turns the category into a command to run in the original project. Mutare deliberately does not execute dependency commands itself: they may use the network or credentials, modify mix.lock, and would write fetched sources into a disposable default sandbox.