feat(astro-config): set site title to 'Nix CN'

- Per Sizhe 'prince213' Zhao:

> 祈園のあ | 天生骄傲, [2025/12/9 08:59]
> 提问 社群实体是叫Nix CN还是Nix/NixOS CN还是NixOS CN比较好（

> Eero Tang, [2025/12/9 08:59]
> Nix CN 吧（

Signed-off-by: Noa Virellia <noa@requiem.garden>

astro.config.mjs

@@ -9,7 +9,7 @@ import mdx from '@astrojs/mdx';
 export default defineConfig({
     integrations: [
         starlight({
-            title: 'NixCN',
+            title: 'Nix CN',
             defaultLocale: 'root',
             logo: {
                 light: './src/assets/nix-cn.svg',