Remove /api prefix from all routes and fix CityId FK constraint

- Strip /api prefix from all endpoint routes
- Make Show.CityId nullable (no longer required FK)
- Drop CityId FK constraint and alter column to NULL at startup via raw SQL
- Add migration MakeCityIdNullable for schema consistency
- Update Show DTOs to reflect nullable CityId

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

PyroFetes/Program.cs

@@ -13,6 +13,23 @@ builder.Services.SwaggerDocument();
 
 var app = builder.Build();
 
+using (var scope = app.Services.CreateScope())
+{
+    var db = scope.ServiceProvider.GetRequiredService<PyroFetesDbContext>();
+    db.Database.ExecuteSqlRaw("""
+        IF EXISTS (
+            SELECT 1 FROM sys.foreign_keys
+            WHERE name = 'FK_Shows_Cities_CityId' AND parent_object_id = OBJECT_ID('Shows')
+        )
+        ALTER TABLE Shows DROP CONSTRAINT FK_Shows_Cities_CityId
+        """);
+    db.Database.ExecuteSqlRaw("""
+        IF COL_LENGTH('Shows', 'CityId') IS NOT NULL
+        AND COLUMNPROPERTY(OBJECT_ID('Shows'), 'CityId', 'AllowsNull') = 0
+            ALTER TABLE Shows ALTER COLUMN CityId INT NULL
+        """);
+}
+
 if (app.Environment.IsDevelopment())
 {
     app.UseSwaggerGen();