Add lot_prefix to products; compose LOT number from prefix + date suffix

Products now have a configurable lot_prefix (e.g. "112"). In the batch form
the prefix is shown read-only next to the suffix input (JJMMTT), and the full
lot_number (e.g. "112-260912") is composed automatically and stored.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

database/migrations/2026_09_12_230000_add_lot_prefix_to_products.php

@@ -0,0 +1,22 @@
+<?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('products', function (Blueprint $table) {
+            $table->string('lot_prefix')->nullable()->unique()->after('title');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('products', function (Blueprint $table) {
+            $table->dropColumn('lot_prefix');
+        });
+    }
+};