Read Turnstile keys from environment variables

Turstile no longer reads the site key from the `turnstile` property of
`nuxt.config.ts`, instead it reads it from the runtime config. I've set
the properties to empty values, as without that they cannot be set using
the environment variables.

The actual keys must now be set via the `NUXT_PUBLIC_TURNSTILE_SITE_KEY`
and `NUXT_TURNSTILE_SECRET_KEY` environment variables.

nuxt.config.ts

@@ -305,6 +305,10 @@ export default defineNuxtConfig({
         // @ts-ignore
         globalThis.CF_PAGES_COMMIT_SHA ||
         'unknown',
+      turnstile: { siteKey: '' },
+    },
+    turnstile: {
+      secretKey: '',
     },
   },
   typescript: {
@@ -362,9 +366,7 @@ export default defineNuxtConfig({
       }
     },
   },
-  turnstile: {
-    siteKey: '0x4AAAAAAAW3guHM6Eunbgwu',
-  },
+  turnstile: {},
   nitro: {
     moduleSideEffects: ['@vintl/compact-number/locale-data'],
   },