🔥 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/factories/CityFactory.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Models\City;
+use App\Models\Country;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<City>
+ */
+class CityFactory extends Factory
+{
+    /**
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        return [
+            'country_id' => Country::factory(),
+            'name' => fake()->city(),
+            'latitude' => fake()->latitude(47, 55),
+            'longitude' => fake()->longitude(6, 16),
+            'osm_relation' => null,
+            'simplified_geojson' => null,
+        ];
+    }
+
+    public function vienna(): static
+    {
+        return $this->state(fn () => [
+            'name' => 'Wien',
+            'latitude' => 48.2082,
+            'longitude' => 16.3738,
+        ]);
+    }
+
+    public function berlin(): static
+    {
+        return $this->state(fn () => [
+            'name' => 'Berlin',
+            'latitude' => 52.5200,
+            'longitude' => 13.4050,
+        ]);
+    }
+
+    public function munich(): static
+    {
+        return $this->state(fn () => [
+            'name' => 'München',
+            'latitude' => 48.1351,
+            'longitude' => 11.5820,
+        ]);
+    }
+
+    public function zurich(): static
+    {
+        return $this->state(fn () => [
+            'name' => 'Zürich',
+            'latitude' => 47.3769,
+            'longitude' => 8.5417,
+        ]);
+    }
+}