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/Client/UI/WorldLauncher.cs

@@ -28,8 +28,8 @@ namespace ProjectM.Client
 
         public static bool Busy { get; private set; }
 
-        /// <summary>Slice 2: the class chosen in the menu (a CharacterId byte), seeded into the client world at session start.</summary>
-        public static byte SelectedClass = (byte)CharacterId.Warrior;
+        /// <summary>Slice 2: the frame chosen in the menu (a FrameKind byte), seeded into the client world at session start.</summary>
+        public static byte SelectedClass = (byte)FrameKind.Warrior;
 
         /// <summary>The mode of the most recently started session — the HUD's outcome banner branches on it
         /// (single: PLAY AGAIN restarts; co-op: the honest exit is a clean teardown for everyone).</summary>