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/JudgeHandler.cs

@@ -15,7 +15,7 @@ internal sealed class JudgeHandler : IFrameHandler
         // start another one, stalling the loop; confirmed by the 2026-06-03 two-client capture).
         // The sender then emits TurnStart, which TurnStartHandler relays to the opponent as {spin}.
         // battleCode is dropped; spin=0 for the deterministic-turn slice.
-        if (ctx.Type == BattleType.Pvp && ctx.BothSidesAfterReady())
+        if (ctx.BothSidesAfterReady())
         {
             var frame = ctx.Env with { Body = new JudgeBody(Spin: BattleFrameDefaults.DeterministicTurnSpin) };
             return new[] { new DispatchRoute(ctx.From, frame, Stock.Normal) };