fix(typst): style CodeArgKey via HighlightStyle, not theme CSS

The tok-attributeName CSS class relies on each theme defining it, but
26 of 41 themes never had it. Defining the colour directly in
typstHighlightStyle (like we do for heading/strong/emphasis) applies
it universally regardless of which theme is active.

Amber #c47900 is legible on both light and dark backgrounds.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/web/frontend/js/features/source-editor/languages/typst/index.ts

@@ -101,8 +101,9 @@ const typstHighlightStyle = HighlightStyle.define([
   { tag: t.heading, fontWeight: 'bold' },
   { tag: t.strong, fontWeight: 'bold' },
   { tag: t.emphasis, fontStyle: 'italic' },
-  // Diagnostic: force arg keys bright red so we can confirm the token reaches the highlighter.
-  { tag: t.attributeName, color: '#cc0000', fontWeight: 'bold' },
+  // Named arg keys (fill:, caption:, columns:…) — amber colour that reads
+  // well on both light and dark backgrounds, independent of theme CSS.
+  { tag: t.attributeName, color: '#c47900' },
 ])
 
 export const typst = () => {