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/DiscordNotificationSettings.php

@@ -34,6 +34,10 @@ class DiscordNotificationSettings extends Model
         'discord_ping_enabled',
     ];
 
+    protected $hidden = [
+        'discord_webhook_url',
+    ];
+
     protected $casts = [
         'discord_enabled' => 'boolean',
         'discord_webhook_url' => 'encrypted',