feat: add WebhookChannel placeholder implementation

Add basic WebhookChannel infrastructure:
- Create SendsWebhook interface
- Create WebhookChannel with placeholder implementation (logs instead of sending)
- Update Test notification to support webhook channel
- Add WebhookChannel to HasNotificationSettings trait
- Add toWebhook() method to Test notification

This provides a working foundation that won't break test notifications.
The actual HTTP webhook delivery will be implemented in a follow-up.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/Notifications/Test.php

@@ -7,6 +7,7 @@ use App\Notifications\Channels\EmailChannel;
 use App\Notifications\Channels\PushoverChannel;
 use App\Notifications\Channels\SlackChannel;
 use App\Notifications\Channels\TelegramChannel;
+use App\Notifications\Channels\WebhookChannel;
 use App\Notifications\Dto\DiscordMessage;
 use App\Notifications\Dto\PushoverMessage;
 use App\Notifications\Dto\SlackMessage;
@@ -36,7 +37,7 @@ class Test extends Notification implements ShouldQueue
                 'telegram' => [TelegramChannel::class],
                 'slack' => [SlackChannel::class],
                 'pushover' => [PushoverChannel::class],
-                'webhook' => [], // WebhookChannel will be implemented later
+                'webhook' => [WebhookChannel::class],
                 default => [],
             };
         } else {
@@ -111,4 +112,13 @@ class Test extends Notification implements ShouldQueue
             description: 'This is a test Slack notification from Coolify.'
         );
     }
+
+    public function toWebhook(): array
+    {
+        return [
+            'event' => 'test',
+            'message' => 'This is a test webhook notification from Coolify.',
+            'url' => base_url(),
+        ];
+    }
 }