fix(webhooks): test endpoint formats payload per platform; add missing column

* The Test URL button was POSTing a generic {event, timestamp, data}
  envelope to every endpoint. Google Chat / Slack / Discord / Teams
  reject anything that isn't their specific shape — so a successful
  Laravel request still got a 400 back from the platform, making the
  test look broken. The real webhook events already handle this via
  WebhookCheckService::formatPayloadForPlatform; that helper is now
  exposed as a public static (buildPlatformPayload) and the test
  endpoint uses the same code path, so the test exercises the same
  format real events will.
* unifi_device_states was missing a consecutive_count column the
  WebhookCheckService inserts on every snapshot capture. The scheduler
  was throwing "Unknown column 'consecutive_count'" once a minute.
  Added an idempotent migration.

v1.6.1.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

database/migrations/2026_05_24_000003_add_consecutive_count_to_unifi_device_states.php

@@ -0,0 +1,26 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('unifi_device_states', function (Blueprint $table) {
+            if (! Schema::hasColumn('unifi_device_states', 'consecutive_count')) {
+                $table->unsignedSmallInteger('consecutive_count')->default(0)->after('in_alert');
+            }
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('unifi_device_states', function (Blueprint $table) {
+            if (Schema::hasColumn('unifi_device_states', 'consecutive_count')) {
+                $table->dropColumn('consecutive_count');
+            }
+        });
+    }
+};