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/tsconfig.json

@@ -0,0 +1,5 @@
+{
+  "extends": "astro/tsconfigs/strict",
+  "include": [".astro/types.d.ts", "**/*"],
+  "exclude": ["dist"]
+}