Adds a Footer component (credit line, repo/buttplug.io links) below main
content on all app pages, with the layout shell now flex-column so it
sticks to the bottom on short pages. Also swaps the display font from
Space Grotesk to Sora (after trying Fraunces, a serif, which didn't fit).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
