feat: initialize opencode project with Astro and Starlight

- Add package.json for project configuration and dependencies
- Create content configuration for Starlight documentation
- Add example guide and reference markdown files
- Create index page for documentation with navigation and next steps
- Set up TypeScript configuration for the project

web/opencode/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() }),
+};