feat: add City model and serializer, update RegionCard and create CityCard component, enhance admin interface for City management

backend/server/worldtravel/migrations/0012_city.py

@@ -0,0 +1,27 @@
+# Generated by Django 5.0.8 on 2025-01-09 15:11
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('worldtravel', '0011_country_latitude_country_longitude'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='City',
+            fields=[
+                ('id', models.CharField(primary_key=True, serialize=False)),
+                ('name', models.CharField(max_length=100)),
+                ('longitude', models.DecimalField(blank=True, decimal_places=6, max_digits=9, null=True)),
+                ('latitude', models.DecimalField(blank=True, decimal_places=6, max_digits=9, null=True)),
+                ('region', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='worldtravel.region')),
+            ],
+            options={
+                'verbose_name_plural': 'Cities',
+            },
+        ),
+    ]