chore: low-friction commitlint (drop cosmetic hard-fails)

[kiro-systemf]

Apply the org-decided low-friction commitlint policy to the repo-root commitlint.config.ts. commitlint change only.

What changed

• subject-full-stop, header-full-stop, body-full-stop -> 0 (off)
• scope-enum -> 0 (off); the static SCOPES enum deleted
• scope-case -> 1 (warn, was error)
• type-matches-diff-shape deleted entirely, along with its plugin rule and all its machinery (stagedFiles(), ALLOWED_BY_SHAPE, the isDoc/isTest/isCI/isLockfile/isTooling/matchesAny matchers, and the node:child_process import)
• body-leading-blank, footer-leading-blank -> 1 (warn, was off)

Kept at error (the real bars)

no-ai-coauthors, type-empty, type-case, type-enum (same 16 entries), subject-empty. The no-ai-coauthors plugin rule and patterns are untouched.

Why

These rules fail a whole commit for cosmetic reasons (a trailing period, an unguessable scope, a heuristic type-vs-diff guess) that have zero release or correctness impact: releases run on changesets (.changeset/*.md), not commit messages. Dropping them stops spurious whole-commit failures on agent commits while keeping the one message policy that matters (the AI-coauthor ban) and tidy log grouping (type).

Verified

With the pinned toolchain (@commitlint/cli@21.2.3, config-conventional@21.2.3):

• printf 'feat: add thing.' | commitlint -> exit 0 (trailing period no longer fails)
• empty type still fails (type-empty)
• AI co-author line still fails (no-ai-coauthors)
• --print-config json confirms every rule level above

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