feat(w3c/style): let an editor turn dark mode off with darkMode: false

[marcoscaceres]

An editor can now set darkMode: false and ReSpec stops offering dark mode for that spec: it emits no dark stylesheet, so W3C's fixup.js finds nothing to toggle, and it strips its own @media (prefers-color-scheme: dark) blocks so a reader whose operating system prefers dark does not land on a light page with dark ReSpec components in it. This matches Bikeshed's Dark Mode metadata, including that second half. Only an explicit false disables anything.

The option is transitional and the documentation says so: custom CSS that is not dark-aware is the thing to fix.

Stacked on #5436, so the base is that branch and the diff shows only this change. No release should go out before the stylesheet work lands.

Gemini wrote the tests from the specification before this implementation existed. I edited two things in them, both noted in the file: a matcher that could never fail against the minified bundle, and an unused import that failed lint.

Written with AI: this change was generated by Claude. Per AI_POLICY.md.

Proof: exporting the same source with each configuration. With darkMode: false the published bytes carry no dark.css link, no preload hint for it, no color-scheme meta, and none of ReSpec's five dark media queries; with the option absent, all five remain and the link is present with disabled="". Marcos then confirmed it manually, including with the operating system set to dark, which is the case the strip exists for.

[Copilot]

Pull request overview

Adds a W3C darkMode: false opt-out that removes ReSpec-provided dark-mode resources and styles.

Changes:

• Adds strict opt-out handling and dark-media-query stripping.
• Documents the transitional configuration option.
• Adds integration coverage and an author-style fixture.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/w3c/style.js	Implements dark-mode opt-out behavior.
src/type-helper.d.ts	Types and documents darkMode.
tests/spec/w3c/dark-mode-opt-out-spec.js	Tests opt-out behavior and preservation.
tests/spec/core/author-dark-style.html	Provides author CSS fixture.

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Pull request overview

Copilot reviewed 3 out of 4 changed files in this pull request and generated 6 comments.