Fix varchar(10) overflow on training_groups.code column

Generated codes like TEAM2001-10 exceed 10 chars when there are 10+ duplicate
program names within an academy. Widen to varchar(20).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

database/migrations/2026_07_17_000001_widen_training_groups_code_column.php

+<?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('training_groups', function (Blueprint $table) {
+            $table->string('code', 20)->change();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('training_groups', function (Blueprint $table) {
+            $table->string('code', 10)->change();
+        });
+    }
+};