fix(api): hide sensitive fields by default

Add model-level hidden fields for secrets, tokens, keys, notification
credentials, deployment logs, and environment values. Allow explicit
read:sensitive API access to reveal gated private keys and deployment logs,
and cover the behavior with feature and unit tests.

app/Models/SslCertificate.php

@@ -20,6 +20,10 @@ class SslCertificate extends Model
         'is_ca_certificate',
     ];
 
+    protected $hidden = [
+        'ssl_private_key',
+    ];
+
     protected $casts = [
         'ssl_certificate' => 'encrypted',
         'ssl_private_key' => 'encrypted',