Refresh marketing pages and docs styling

[lklynet]

Summary

• Redesigned the landing page with a new hero, feature sections, integration cards, and updated screenshots/branding.
• Reworked the Spotify import and flows/playlists docs into cleaner, more interactive layouts with tabbed JSON examples.
• Updated shared styles, navigation, and icon assets to support the new visual system across the public site.

Testing

• Not run
• Reviewed the updated HTML/CSS structure for the landing page and docs pages.
• Checked that external links now include safer rel="noopener noreferrer" attributes where applicable.