LANTERN purge B7: rename CharacterId -> FrameKind (frame terminology)

Enum renamed in StatIds.cs (byte values unchanged - serialized definitions/saves
never re-mean); all call sites + doc mentions swept (ClassTraits, PlayerAuthoring,
CharacterStatsDefinition field type, menu/UI, tests). CharacterStatsDefinition SO
CLASS name kept (asset-binding risk; deferred per plan). 390 green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Assets/_Project/Scripts/Simulation/Connection/GoInGameRequest.cs

@@ -7,5 +7,5 @@ namespace ProjectM.Simulation
     /// NetworkStreamInGame to the connection (enabling snapshot/command flow) and spawns the
     /// client's player ghost. Lives in Simulation so both worlds see the type for RPC source-gen.
     /// </summary>
-    public struct GoInGameRequest : IRpcCommand { public byte ClassId; } // Slice 2: per-player class (CharacterId byte; 0 -> server defaults to Warrior)
+    public struct GoInGameRequest : IRpcCommand { public byte ClassId; } // Slice 2: per-player class (FrameKind byte; 0 -> server defaults to Warrior)
 }