fix: require explicit CDN_ENABLED for CDN mode

CDN no longer auto-enables via subdomain config. Requires
CDN_ENABLED=true in .env to prevent unexpected CDN URL generation.

Co-Authored-By: Virgil <virgil@lethean.io>

src/Core/Helpers/Cdn.php

@@ -52,14 +52,12 @@ class Cdn
     /**
      * Check if CDN mode is enabled.
      *
-     * CDN is considered enabled if:
-     * - External CDN URL is configured, OR
-     * - CDN subdomain is configured (default)
+     * Requires explicit CDN_ENABLED=true in .env.
+     * Without it, all assets use the standard asset() helper.
      */
     public static function isEnabled(): bool
     {
-        return config('cdn.enabled', false)
-            || config('core.cdn.subdomain');
+        return (bool) config('cdn.enabled', false);
     }
 
     /**