fix(ranked-ai): randomize bot selection and seed for AI fallback matches

Bot roster pick was hashing (UserName, ClassId) — same player always
faced the same bot class. Now hashes battleId so different matches get
different opponents while retries of the same pending battle stay
consistent.

AI start response hardcoded Seed=0 for both sides, so the client's
deck shuffle/mulligan/draw RNG was deterministic every match. The
BattleNode's per-battle MasterSeed (Random.Shared) was never sent to
bot-mode clients because InitBattleHandler skips the Matched frame.
Now populates Seed with Random.Shared.Next() on the HTTP response.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Controllers/RankBattleController.cs

@@ -162,7 +162,8 @@ public sealed class RankBattleController : ControllerBase
         }
         var selfCtx = pending.P1.Context;
 
-        var bot = await _botRoster.PickAsync(selfCtx, ct);
+        var bot = await _botRoster.PickAsync(selfCtx, pending.BattleId, ct);
+        var seed = Random.Shared.Next();
 
         // Per spec, ai-start.md TODO: turnState semantics unclear. Default 0 (player first).
         return Ok(new AiBattleStartResponseDto
@@ -179,7 +180,7 @@ public sealed class RankBattleController : ControllerBase
                 FieldId = selfCtx.FieldId,
                 IsOfficial = selfCtx.IsOfficial,
                 OppoId = bot.AiId,
-                Seed = 0,
+                Seed = seed,
                 Rank = 0,
                 BattlePoint = 0,
                 ClassId = int.TryParse(selfCtx.ClassId, out var cId) ? cId : -1,
@@ -197,7 +198,7 @@ public sealed class RankBattleController : ControllerBase
                 FieldId = bot.FieldId,
                 IsOfficial = bot.IsOfficial,
                 OppoId = (int)vid,
-                Seed = 0,
+                Seed = seed,
                 Rank = bot.Rank,
                 BattlePoint = bot.BattlePoint,
                 ClassId = bot.ClassId,