fix(load): only resolve relative formatter paths (#4761)

* fix(load): only resolve relative formatter paths

resolveFrom() returns an absolute path on success, which leaks the
internal package location into the loaded config when the formatter
is a package specifier (e.g. "@commitlint/format"). Under yarn's
flat node_modules layout the resolution typically failed and the
specifier was preserved by accident; under stricter resolution
(pnpm, npm with hoisting disabled) it succeeds and the absolute
path appears in config output.

Skip resolveFrom for non-relative specifiers and let the runtime
resolve them via standard module resolution at import time.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs(load): clarify resolveFormatter handles only relative paths

Address review feedback: the previous wording "relative/custom" was
misleading because absolute paths and package specifiers both skip
resolveFrom and pass through unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>