flatten monorepo, migrate off Vercel

- Remove penfield (split to own repo on Forgejo)
- Move www/ contents to root, rename to wynne.rs
- Swap @astrojs/vercel for @astrojs/node, upgrade to Astro 6
- Remove auth-astro/GitHub OAuth (TinyAuth at proxy layer)
- Remove Vercel deploy webhook
- Switch to local SQLite DB (drop Turso)
- Update generate-stats.js for new build output paths

src/lib/api.ts

@@ -0,0 +1,10 @@
+export function jsonResponse(data: unknown, status = 200): Response {
+  return new Response(JSON.stringify(data), {
+    status,
+    headers: { 'Content-Type': 'application/json' },
+  });
+}
+
+export function errorResponse(message: string, status: number): Response {
+  return jsonResponse({ error: message }, status);
+}