doc: lint according to @node-core/remark-lint

[avivkeller]

This PR lints the documentation according to https://www.npmjs.com/package/@node-core/remark-lint, which'll be the linter associated with the new tooling.

The difference which are rectified by this PR:

• The linter requires one PR URL per change
• The linter disallows duplicate stability nodes
• The linter requires full 40-character commits

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[Copilot]

Pull request overview

This PR updates the documentation linting tooling from remark-preset-lint-node to @node-core/remark-lint and fixes various formatting issues identified by the new linter to ensure documentation consistency across the Node.js project.

Key changes:

• Migrated linting infrastructure to use @node-core/remark-lint with separate API and base linters
• Standardized horizontal rule syntax from *** to --- throughout documentation
• Normalized type union syntax by removing spaces (e.g., string | null → string|null)

Reviewed changes

Copilot reviewed 15 out of 28 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tools/lint-md/package.json	Updated dependencies to use @node-core/remark-lint and remark instead of remark-preset-lint-node, remark-parse, remark-stringify, and unified
tools/lint-md/lint-md.mjs	Refactored to use new linter API with separate processors for API docs and base docs, imports type-map.json, simplified error reporting logic
doc/contributing/releases.md	Replaced *** with --- for horizontal rules
doc/contributing/collaborator-guide.md	Replaced *** with --- for horizontal rules
doc/changelogs/CHANGELOG_V15.md	Replaced *** with --- for horizontal rules
doc/changelogs/CHANGELOG_V12.md	Replaced *** with --- for horizontal rules
doc/changelogs/CHANGELOG_IOJS.md	Replaced *** with --- for horizontal rules
doc/api/util.md	Removed spaces in union type annotations
doc/api/url.md	Removed spaces in union type annotations
doc/api/type-map.json	Added new file mapping type names to documentation URLs for the linter
doc/api/test.md	Removed spaces in union type annotations
doc/api/stream.md	Collapsed multi-line type annotations to single lines, removed spaces in union types
doc/api/sqlite.md	Removed spaces in union type annotations, converted link-style references to inline type references, removed self-referential link
doc/api/process.md	Removed spaces in union type annotations
doc/api/modules.md	Removed spaces in union type annotations
doc/api/module.md	Removed duplicate stability node
doc/api/inspector.md	Removed duplicate stability node
doc/api/https.md	Removed spaces in union type annotations
doc/api/http2.md	Removed spaces in union type annotations
doc/api/http.md	Removed spaces in union type annotations
doc/api/errors.md	Extended short commit hash to full 40-character format
doc/api/dns.md	Removed spaces in union type annotations
doc/api/diagnostics_channel.md	Removed spaces in union type annotations
doc/api/deprecations.md	Separated combined pr-url array into individual version entries with distinct pr-urls
doc/api/crypto.md	Removed spaces in union type annotations
doc/api/buffer.md	Removed spaces in union type annotations
doc/README.md	Replaced *** with --- for horizontal rules

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[avivkeller]

Blocked by #57343