refactor(battlenode): key dispatch on OpponentIsAckOnly, drop per-frame BattleType switch

Behavior-identical; 231 BattleNode tests green with ZERO test changes.

The 10 handler arms no longer switch on BattleType:
- 4 Bot arms gate on the new FrameDispatchContext.OpponentIsAckOnly
  (Other is not IHasHandshakePhase) — the participant property the audit asked for.
- 6 relay arms drop the Type == Pvp guard; it was redundant with BothSidesAfterReady()
  (only a two-real-player session has both handshake phases). Its doc now records that.
- FrameDispatchContext.Type removed (+ the Type = Type in BuildContext). BattleSession.Type
  stays for the session-level drop cascade.

Zero test churn because the stubs already encode the split: FakeRealParticipant/ProbeParticipant
implement IHasHandshakePhase, the bot stub FakeParticipant doesn't, and NewBotSession uses it as
the opponent.

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

SVSim.BattleNode/Sessions/Dispatch/Handlers/TurnEndHandler.cs

@@ -8,14 +8,14 @@ internal sealed class TurnEndHandler : IFrameHandler
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
         // case 4: Bot — Judge to sender only (no real opponent; client flips back to its local AI).
-        if (ctx.Type == BattleType.Bot && ctx.SenderIsAfterReady)
+        if (ctx.OpponentIsAckOnly && ctx.SenderIsAfterReady)
             return new[] { new DispatchRoute(ctx.From, BattleFrames.BuildJudgeBroadcast(), Stock.Normal) };
 
         // case 8: general AfterReady arm — PvP forwards a {turnState} TurnEnd to the opponent
         // (handover gate). Any non-Pvp non-Bot type that reaches AfterReady consumes the frame.
         if (ctx.SenderIsAfterReady)
         {
-            if (ctx.Type == BattleType.Pvp && ctx.BothSidesAfterReady())
+            if (ctx.BothSidesAfterReady())
             {
                 // Opponent sees {turnState}; receiving TurnEnd drives ITS SendJudge (handover gate):
                 // the opponent (the turn taker-over) then sends a Judge, which JudgeHandler reflects