2.0.0: one import, a letter grade, and a CLI

[IgnaceMaes]

Reworks the public interface around the calls people actually make, puts a letter on the grade, and ships the grade as a CLI. Carries a major changeset, so merging opens the version PR that cuts 2.0.0.

What changes

• npx mailgrade acme.com. The package has a bin: the grade in a terminal (letter, verdict, per-mechanism headlines, and the fixes), with --json for scripts and --strict for CI, where a non-zero exit catches the day someone "temporarily" weakens the DMARC record. Zero dependencies, like everything else here.
• A letter on the grade. DomainGrade carries letter, "A+" down to "F". The verdict sets the band and the details move within it; +all is an automatic F. The rubric lives in spec/grade.json, so ports share it.
• One import. gradeDomain, verifyMessage and analyzeHeaders are on mailgrade itself. Every existing entry point still resolves; the subpaths are now for narrowing a bundle, not for finding the API.
• No setup. resolver is optional everywhere it was required, defaulting to DNS over HTTPS. A Node service that wants the system resolver still passes nodeResolver() from mailgrade/node-dns.
• Headers you can use. verifyMessage takes mta and returns authResults and headers: a folded, CRLF-terminated Received-SPF and Authentication-Results block, ready to prepend. Embedded values come off the wire, so they are sanitised on the way in, and the folder is quote-aware.
• Prose pass. Em dashes, -- stand-ins and a stray … are gone from the docs and comments across the repo.

Breaking

• The root barrel is a curated list rather than export *, so roughly 25 internals no longer appear on mailgrade. Each is still exported from the entry point for its own area.
• The JSON conformance corpus is no longer published in the tarball, and the mailgrade/spec/* subpath is gone with it. The corpus stays in the repository.
• checkDomain is now gradeDomain; the pure function that held that name is now gradeRecords. DohOptions is now GradeDomainOptions.

Checks

pnpm check is green locally: oxlint, tsc, 288 tests across 10 files, tsdown build, publint, and attw --profile node16 (all entry points 🟢 for CJS, ESM and bundler).

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