Refactor: Enforce type safety, fix close deadlock, implement assignee restrictions and notify admin fallbacks

database/migrations/2026_05_20_140000_add_department_id_to_users_table.php

@@ -0,0 +1,27 @@
+<?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('users', function (Blueprint $table) {
+            $table->foreignId('department_id')
+                ->nullable()
+                ->after('role')
+                ->constrained('departments')
+                ->nullOnDelete();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('users', function (Blueprint $table) {
+            $table->dropForeign(['department_id']);
+            $table->dropColumn('department_id');
+        });
+    }
+};