Fix duplicate is_admin migration class conflict

Both migration files shared the same class name causing a
"Class not found" error on fresh migrate runs. Made the first
(empty) file a true no-op and guarded the second with
Schema::hasColumn to safely skip if the column already exists.

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

database/migrations/2025_08_10_020525_add_is_admin_to_users_table.php

@@ -0,0 +1,18 @@
+<?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
+    {
+        // Duplicate of 2025_08_10_162556 — intentionally empty
+    }
+
+    public function down(): void
+    {
+        //
+    }
+};

database/migrations/2025_08_10_162556_add_is_admin_to_users_table.php

@@ -11,10 +11,12 @@ return new class extends Migration
      */
     public function up(): void
     {
+        if (!Schema::hasColumn('users', 'is_admin')) {
             Schema::table('users', function (Blueprint $table) {
                 $table->boolean('is_admin')->default(false)->after('password');
             });
         }
+    }
 
     /**
      * Reverse the migrations.