feat(justfile): add ci, doc, outdated, audit recipes

[sksizer]

Summary

• `ci`: convenience recipe that runs `full-check` + `test`, mirroring CI locally with one command.
• `doc` / `doc-open`: build (and optionally open) `cargo doc --no-deps`.
• `outdated`: surface dependencies with newer versions available (requires `cargo-outdated`).
• `audit`: check dependencies for known security advisories (requires `cargo-audit`).

Test plan

• `just ci` runs format-check, clippy, and tests
• `just doc` builds docs without deps
• `just outdated` works after `cargo install cargo-outdated`
• `just audit` works after `cargo install cargo-audit`