feat(events): support event cover attachments

database/migrations/2026_09_18_000900_add_attachment_id_to_events.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('events', function (Blueprint $table): void {
+            $table->foreignId('attachment_id')->nullable()->constrained('attachments')->nullOnDelete();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('events', function (Blueprint $table): void {
+            if (Schema::getConnection()->getDriverName() !== 'sqlite') {
+                $table->dropForeign(['attachment_id']);
+            }
+
+            $table->dropColumn('attachment_id');
+        });
+    }
+};