Split API into phase-specific endpoint files

Program.cs

@@ -52,6 +52,10 @@ app.UseStaticFiles();
 app.UsePlayerIdentity();
 
 app.MapHealthChecks();
-app.MapApi();
+app.MapStateEndpoints();
+app.MapSuggestEndpoints();
+app.MapVoteEndpoints();
+app.MapResultsEndpoints();
+app.MapAdminEndpoints();
 
 app.Run();