Make reader mode easier to test with fixtures

[culpen90]

Why

Reader mode is implemented as a sizable JavaScript extraction and rendering script embedded in Sources/Quartz/QuartzApp.swift. It works for many article pages, but changes are hard to review because there are no fixtures or repeatable extraction tests.

Where to start

• Sources/Quartz/QuartzApp.swift
• The enterReaderModeScript and exitReaderModeScript constants
• A new test fixture directory, if useful

Suggested approach

Make reader mode more testable without changing its user-facing behavior. Options include moving the JavaScript into a separate bundled resource, adding HTML fixtures, and adding tests that run the extraction logic against representative article pages.

Good fixtures would include:

• a simple article with headings and paragraphs
• an article with images and captions
• a page with nav/sidebar/comment content that should be removed
• a short page that should be rejected as too short

Acceptance criteria

• Reader mode JavaScript is easier to review than one large embedded Swift string, or it has fixture coverage that makes changes safer.
• Fixtures cover at least three page shapes.
• Tests or documented manual checks verify that article content is kept and obvious junk is removed.
• Existing reader mode behavior remains available from the toolbar and View menu.
• swift build succeeds.

Testing

• Run any new reader-mode tests.
• Run swift build.
• Manually open at least one article page and confirm Reading Mode still enters and exits correctly.