Rewrite landing page

[Che-Zhu]

Summary

• Rewrite the landing page around the selected “Ship AI workspaces, not prompts” hero direction.
• Replace the old split terminal demo with a static product landing composition and cropped 3D concept asset.
• Remove the lower trusted-logo/features band per browser annotation feedback.
• Update landing metadata for the v3 dedicated workspace direction.

Validation

• corepack pnpm lint
• corepack pnpm build