Add canvas zoom effects and intro/outro overlays to onboarding flow

When Get Started is clicked: landing page UI fades out, "Let's Learn
About You..." text fades in, canvas zooms to 2.5x with background
nodes dimming, then the onboarding form appears. Each completed step
spawns colored knowledge graph nodes that fly in and connect. On
finish, "Welcome to Sapling" text appears, canvas zooms to 5.5x with
a white overlay transition into dashboard. Closing the flow zooms back
out smoothly with nodes fading. Removed frosted glass backdrop from
OnboardingFlow since the zoomed canvas serves as the visual backdrop.

Author: Jose Cruz