feat(arena-tk2): SoloDefaultsToScripted config flag for dev convenience

Adds BattleNodeOptions.SoloDefaultsToScripted (default false). When true,
the TK2 do_matching controller treats every solo poll as if ?scripted=1
were passed and returns a Scripted 3004 match immediately — useful for
the live client (which can't append query params) to drive the scripted
bot without needing a second player.

Toggle via "BattleNode:SoloDefaultsToScripted" in appsettings*.json
(Program.cs now binds the BattleNode section over the AddBattleNode
defaults). Turn off to test real PvP with two clients.

Trade-off documented on the option: while on, two simultaneous pollers
each get their own Scripted match instead of pairing, so PvP is
effectively disabled until the flag is flipped.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Program.cs

@@ -124,6 +124,9 @@ public class Program
             // Matches the prod do_matching wire format: host:port/socket.io/, no scheme prefix.
             // BestHTTP's SocketManager parses this as the Socket.IO v2 endpoint URL.
             opt.NodeServerUrl = "localhost:5148/socket.io/";
+            // Any field in BattleNodeOptions can be overridden via the "BattleNode" section
+            // in appsettings*.json — see appsettings.Development.json for SoloDefaultsToScripted.
+            builder.Configuration.GetSection("BattleNode").Bind(opt);
         });
         // In-process FCFS pair-up for TK2 PvP /do_matching. Singleton: per-mode state is
         // process-wide. Proper queue API is a separate spec; this is enough to actually