Slice 2 (WIP): class carrier (GoInGameRequest.ClassId) + Warrior cone archetype

The per-player class travels on GoInGameRequest.ClassId (client reads a ClassSelection
singleton); GoInGameServerSystem seeds the class at spawn via ClassTraits (AbilityRef +
permanent trait StatModifiers on a reserved ClassSourceId; CharacterStatsRef stays Default
so the DRG-asymmetry deltas ride the replicated OwnerSendType.All buffer). AbilityFireSystem
gains the aim-directed Cone archetype: cooldown predicted both worlds, server-only cone
damage to living enemies (same-tick, SourceTick-stamped, like the melee cleave). 345/345.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/_Project/Scripts/Simulation/Combat/ClassSelection.cs

@@ -0,0 +1,16 @@
+using Unity.Entities;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// Slice 2: the local player's chosen class (a <see cref="CharacterId"/> byte), staged in the CLIENT world as a
+    /// singleton by the menu / WorldLauncher before going in-game. <see cref="GoInGameRequest"/> picks it up
+    /// (GoInGameClientSystem) so the server seeds the right class at spawn. NOT replicated — it is client-local
+    /// intent; the class travels to the server via the RPC, then back to all clients via the seeded StatModifiers +
+    /// the replicated AbilityRef. 0 = unset (the server defaults to Warrior).
+    /// </summary>
+    public struct ClassSelection : IComponentData
+    {
+        public byte ClassId;
+    }
+}