Add Campaigns module for grouping QR codes.

Let accounts organise codes by promo or launch, attach or detach codes, and view combined scan totals from the sidebar.

database/migrations/2026_07_16_100000_create_campaigns_table.php

@@ -0,0 +1,37 @@
+<?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::create('campaigns', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('user_id')->constrained()->cascadeOnDelete();
+            $table->string('name');
+            $table->text('description')->nullable();
+            $table->string('status', 20)->default('active')->index();
+            $table->timestamp('starts_at')->nullable();
+            $table->timestamp('ends_at')->nullable();
+            $table->timestamps();
+
+            $table->index(['user_id', 'status']);
+        });
+
+        Schema::table('qr_codes', function (Blueprint $table) {
+            $table->foreignId('campaign_id')->nullable()->after('user_id')->constrained('campaigns')->nullOnDelete();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('qr_codes', function (Blueprint $table) {
+            $table->dropConstrainedForeignId('campaign_id');
+        });
+
+        Schema::dropIfExists('campaigns');
+    }
+};