Upgrade to Astro 6.1.9 and migrate to content layer API

Moves content config from src/content/config.ts to src/content.config.ts
with glob loaders as required by Astro 6. Replaces entry.slug with entry.id
and entry.render() with render(entry) throughout. Removes legacy collections
option from astro.config.mjs.

astro.config.mjs

@@ -30,6 +30,5 @@ remarkPlugins[1][1].resolveEmbedContent = resolveEmbedContent;
 export default defineConfig({
   site: 'https://wiki.bincio.com',
   integrations: [sitemap(), tailwind(), svelte()],
-  legacy: { collections: true },
   markdown: { remarkPlugins },
 });