perf(fonts): trim Google Fonts to weights in use

Narrowed the Cormorant Garamond request to 600 only and Manrope to
400/600/700/800, removing the unused 500 and 700 variants. Added
font-weight: 600 to .final-cta h2 so the heading explicitly uses
the retained weight.

Co-Authored-By: Claude <[email protected]>