Remove the vendored swiML stylesheet pipeline

[cjdyer]

This PR simplifies how SwimDSL handles swiML.css by relying on the stylesheet URL emitted by the upstream swiML transform instead of rewriting preview output to a local generated file.

Changes:

• Stop rewriting rendered HTML from the upstream stylesheet URL to ./swiML.css
• Remove the prepare-time CSS/font download pipeline
• Drop the unused css and @types/css dev dependencies
• Document that prepare now refreshes only the upstream XSLT/SEF assets
• Mark local public/swiML.css and public/fonts/ artifacts as legacy ignored assets for existing worktrees

Why:

• Reduces architectural confusion for new contributors by making it clear that the stylesheet is owned upstream
• Removes repo-local tooling that existed only to support the stylesheet rewrite
• Shrinks dependency and maintenance surface area

[cjdyer]

For an exported html document.

Before:

After:

[hazzery]

We manually tested on the branches with Cory's branch and all seemed well