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/pages/sitemap.txt.ts

@@ -0,0 +1,21 @@
+import { getCollection } from 'astro:content';
+import type { APIContext } from 'astro';
+import { getSlug } from '../lib/posts';
+import { getTxtFiles } from '../lib/txt';
+import { SUBDOMAINS } from '../lib/consts';
+
+export async function GET(context: APIContext) {
+  const site = context.site?.origin ?? 'https://wynne.rs';
+  const posts = await getCollection('posts');
+  const txtFiles = getTxtFiles().map(f => f.name);
+
+  const urls = [
+    '/',
+    ...posts.map(post => `/${getSlug(post.id)}`),
+    ...txtFiles.map(txt => `/${txt}`),
+  ].map(p => `${site}${p}`);
+
+  return new Response([...urls, ...SUBDOMAINS].join('\n'), {
+    headers: { 'Content-Type': 'text/plain' },
+  });
+}