fix(matchmaking): deploy signal targets only the deploying player

EnterMatchmakingMatch broadcast OnSquadMatchmakingSuccess to Clients.All,
so one player deploying pulled every connected player into the match.
Map each player to their SignalR connection (GetSignalRConnection tags the
URL with uid; CycleHub records it via a SignalRConnectionRegistry) and
send the deploy signal only to that connection (broadcast fallback if
unmapped). Also enable m_automaticImportPlatformFriends (Steam friends).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Prospect.Server.Api/Startup.cs

@@ -36,6 +36,7 @@ public class Startup
         services.AddSingleton<DbUserDataService>();
 
         services.AddSingleton<Prospect.Server.Api.Services.Squad.SquadService>();
+        services.AddSingleton<Prospect.Server.Api.Hubs.SignalRConnectionRegistry>();
 
         services.AddHostedService<QosService>();
         services.AddSingleton<QosServer>();