[subygan]

Brings the README in line with the getparsec site's parsec page.

• Hero: the site's hero illustration, the heading "A new way to go farther.", and the new narrative paragraph
• Links to install, sign in, and the benchmark; badges in the site's black and mint green
• "Cheaper. Faster. More solved.": SWE-bench Verified results from the site (−39% cost, −25% time, 62/100 solved), with the method note and a link to the benchmark
• "How it works": the four steps from the site, each with its illustration
• The install, data-disclosure, layout, self-host, build, and invariants sections are unchanged

Illustrations are in assets/brand/site/, each in a dark and a light version. The solid backgrounds were removed, and the light versions flip the colors and darken the accent green so it reads on white.