ARCH-2: apply EF migrations on startup in Development

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

GerbilManagerWebAPI/Program.cs

@@ -23,6 +23,10 @@ if (app.Environment.IsDevelopment())
 {
     app.UseSwagger();
     app.UseSwaggerUI();
+
+    // Aspire provisions an empty database in dev — bring the schema up to date.
+    using var scope = app.Services.CreateScope();
+    scope.ServiceProvider.GetRequiredService<ApplicationContext>().Database.Migrate();
 }
 
 if (app.Environment.IsDevelopment())