fix: revert to working vercel.json config (#438)

Remove root vercel.json that was causing 404 errors on all routes.
Restore app/vercel.json to its original working state with the SPA
fallback rewrite.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <[email protected]>

Author: MaxGhenis

.gitignore

@@ -71,4 +71,5 @@ __pycache__/
 .Python
 env/
 venv/
-.venv
+.venv
+.vercel

app/vercel.json

@@ -1 +1,3 @@
-{}
+{
+  "rewrites": [{ "source": "/(.*)", "destination": "/" }]
+}