feat: implement actual webhook delivery

Implement full webhook delivery functionality:
- Create SendWebhookJob to handle HTTP POST requests
- Update WebhookChannel to dispatch webhook jobs
- Configure retry logic (5 attempts, 10s backoff)
- Update Test notification payload with success/message structure

Webhook payload structure:
{
  "success": true/false,
  "message": "notification message",
  "event": "event_type",
  "url": "coolify_dashboard_url"
}

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

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

app/Jobs/SendWebhookJob.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace App\Jobs;
+
+use Illuminate\Bus\Queueable;
+use Illuminate\Contracts\Queue\ShouldBeEncrypted;
+use Illuminate\Contracts\Queue\ShouldQueue;
+use Illuminate\Foundation\Bus\Dispatchable;
+use Illuminate\Queue\InteractsWithQueue;
+use Illuminate\Queue\SerializesModels;
+use Illuminate\Support\Facades\Http;
+
+class SendWebhookJob implements ShouldBeEncrypted, ShouldQueue
+{
+    use Dispatchable, InteractsWithQueue, Queueable, SerializesModels;
+
+    /**
+     * The number of times the job may be attempted.
+     *
+     * @var int
+     */
+    public $tries = 5;
+
+    public $backoff = 10;
+
+    /**
+     * The maximum number of unhandled exceptions to allow before failing.
+     */
+    public int $maxExceptions = 5;
+
+    public function __construct(
+        public array $payload,
+        public string $webhookUrl
+    ) {
+        $this->onQueue('high');
+    }
+
+    /**
+     * Execute the job.
+     */
+    public function handle(): void
+    {
+        Http::post($this->webhookUrl, $this->payload);
+    }
+}