Print a copyable cargo add command for generated dependencies #31

Goal

Make the post-generation dependency step easier while keeping REQUIRED_DEPS.toml authoritative and never editing a consumer manifest automatically.

Scope

Render deterministic cargo add command(s) from the same DepRequirement collection used for REQUIRED_DEPS.toml, then show them in normal successful CLI output. Quiet and JSON modes must keep their current output contracts.

Acceptance criteria

• Versions and feature lists come from the existing dependency collector, not a second hardcoded table.
• Output ordering is deterministic.
• Dependencies without features and dependencies with multiple features are both covered by unit tests.
• The command is shell-copyable for the supported crate names/features.
• The generator still does not modify Cargo.toml.
• README explains that the command and fragment are alternatives.

A single command per dependency is acceptable if that keeps quoting and feature handling straightforward.