Refactor WEBMENTION_TOKEN handling: read from file and remove environment configuration

astro.config.mjs

@@ -2,7 +2,7 @@
 
 import mdx from '@astrojs/mdx';
 import sitemap from '@astrojs/sitemap';
-import { defineConfig, envField, fontProviders } from 'astro/config';
+import { defineConfig, fontProviders } from 'astro/config';
 
 import node from '@astrojs/node';
 
@@ -10,16 +10,6 @@ import node from '@astrojs/node';
 export default defineConfig({
   site: 'https://adrian-altner.de',
 
-  env: {
-    schema: {
-      WEBMENTION_TOKEN: envField.string({
-        context: 'server',
-        access: 'secret',
-        optional: true,
-      }),
-    },
-  },
-
   devToolbar: {
       enabled: false,
 	},