Add dual-screen customer display for the register.

Token-gated full-screen customer view shows order, payment QR, tips,
signature, receipt, and promo phases while the till keeps operator UI.

database/migrations/2026_07_15_160000_create_pos_customer_displays_table.php

@@ -0,0 +1,28 @@
+<?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('pos_customer_displays', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('location_id')->unique()->constrained('pos_locations')->cascadeOnDelete();
+            $table->string('owner_ref', 64)->index();
+            $table->string('token', 64)->unique();
+            $table->string('phase', 32)->default('idle');
+            $table->json('payload')->nullable();
+            $table->json('customer_action')->nullable();
+            $table->timestamp('last_pushed_at')->nullable();
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('pos_customer_displays');
+    }
+};