Refactor CLI into modular structure

[0xpantera]

Summary

• move clap structs to new cli.rs
• introduce Config for global flags
• split command handlers into modules under commands/
• update workflows to use Config
• slim down lib.rs to command dispatch layer
• add shared helper and smoke test
• propagate --pkg flag through build_nargo_args
• clean up logging setup

Testing

• RUSTFLAGS="-D warnings" cargo check --workspace --all-targets --all-features --locked
• cargo clippy --workspace --all-targets --all-features -- -D warnings (fails: 'cargo-clippy' not installed)
• cargo test
• cargo run --quiet -- check (fails: cannot find a Nargo.toml)

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https://chatgpt.com/codex/tasks/task_e_685ba97fb2a083298f365c67e64f81b1