fix(website): stop category-page heading from wrapping

The results-intro grid (1fr + 28rem note column) squeezed the heading on
category pages with long names, e.g. "Python Projects in Environment
Management" wrapped onto two lines.

Scope a single-column override to .category-results so the heading takes
the full row and the note drops below right-aligned. Index page layout
is untouched since its heading is short.