feat(docs): new terminal-window logo and refined prompt favicon

Replaces the minimal single-color >_ mark with a two-tone Python palette
(#4B8BBE blue + #FFD43B yellow):

- logo.svg: a rounded dark terminal window with traffic-light dots and a
  yellow prompt + blue cursor inside (richer header/social-card mark).
- favicon.svg: a bolder standalone >_ prompt that stays legible at 16px.

mkdocs already points theme.logo/theme.favicon at these paths, and the
Material social plugin regenerates OG cards from the logo in CI, so no config
change is needed.

Author: abhiksark