chore: scaffold Astro Starlight project

- Astro 6.3 + Starlight 0.39
- TypeScript strict
- Sitemap integration
- Inter + JetBrains Mono variable fonts
- Custom .gitignore (no AI artifacts; no .env)
- .editorconfig

src/content.config.ts

@@ -0,0 +1,7 @@
+import { defineCollection } from 'astro:content';
+import { docsLoader } from '@astrojs/starlight/loaders';
+import { docsSchema } from '@astrojs/starlight/schema';
+
+export const collections = {
+	docs: defineCollection({ loader: docsLoader(), schema: docsSchema() }),
+};