Add site footer and switch display font to Sora, bump to 0.5.0

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>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sexy",
-  "version": "0.4.0",
+  "version": "0.5.0",
   "private": true,
   "scripts": {
     "dev": "next dev",