Manage webhooks from the panel

Create one and see its secret once, send a test, change the secret, and read
each delivery with what the other end answered.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/Rules/PublicHttpsUrl.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Rules;
+
+use App\Support\Webhooks\PublicEndpoint;
+use Closure;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+/**
+ * An HTTPS address whose host resolves only to public addresses — somewhere
+ * this server may send a request to without reaching into its own network.
+ */
+class PublicHttpsUrl implements ValidationRule
+{
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        [, $reason] = app(PublicEndpoint::class)->check((string) $value);
+
+        if ($reason !== null) {
+            $fail(__("rules.media.remote.{$reason}"));
+        }
+    }
+}