docs: migrate documentation from VitePress to Starlight (#361)

- Replace VitePress with Astro Starlight for documentation
- Reorganize document structure with better hierarchy
- Split large documents into sub-modules for better readability
- Add new sections: component, entity-query, serialization, system
- Support both Chinese (default) and English documentation
- Add responsive design and improved navigation

docs/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() }),
+};