🔥 Add initial database migrations, seeders, and factories

🎨 Refactor `Lecturer` model to include new fields and factory usage
🔧 Update `DatabaseSeeder` to handle default seeds
🛠️ Enhance `einundzwanzig` database configuration for SQLite compatibility

database/migrations/2026_05_02_155302_create_cities_table.php

@@ -0,0 +1,29 @@
+<?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('cities', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('country_id')->constrained()->cascadeOnDelete();
+            $table->string('name');
+            $table->string('slug')->nullable()->index();
+            $table->decimal('latitude', 10, 7)->nullable();
+            $table->decimal('longitude', 10, 7)->nullable();
+            $table->json('osm_relation')->nullable();
+            $table->json('simplified_geojson')->nullable();
+            $table->unsignedBigInteger('created_by')->nullable();
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('cities');
+    }
+};