Enable clippy::dbg_macro lint #86

Summary

Enable the clippy::dbg_macro restriction lint (set to deny) in the [lints.clippy] table.

What it catches

clippy::dbg_macro flags any use of the dbg!() macro left in the source. dbg!() is a debugging aid that prints to stderr and is almost never intended to ship — it produces noisy, unstructured output and bypasses the project's normal logging/UI paths.

Why it improves code quality

• Prevents accidental debugging artifacts from being committed and reaching production.
• Keeps stderr output intentional and consistent with the tool's UX.
• Fits this repo's existing strict, deny-by-default posture (pedantic/nursery/cargo already denied, unsafe_code forbidden).

dbg_macro lives in the restriction group, so it is not covered by any group already enabled here — this is a genuinely new check.

Noise

There are currently 0 violations across the lib, binary, and all test targets, so enabling it is a zero-churn config change that guards against future regressions.

A PR implementing this follows.