Rebrand: Vello is now memsprout

A new look and a new name. The product is now memsprout — the shared AI-context layer for teams. This ships a fresh design system (Geist typography, a calm cool-neutral palette with a Moss green accent, and a reserved violet that marks anything captured by an AI agent), a light/dark theme toggle, and a rebuilt component set across every screen. Each Memory now shows quiet provenance — who captured it, you or an agent. New Owner setup: a guided checklist and a space-setup wizard that takes you from zero to a Shared Space with Topics and invited teammates. The product's internal database schema was also renamed end-to-end; existing AI-client connections keep working unchanged.