v0.2.0 transitioned to api-only, extended and improved features, docs and tests added

internal/core/error.go

@@ -0,0 +1,15 @@
+// FILE: internal/core/core.go
+package core
+
+// Error codes
+const (
+	ErrGameNotFound      = "GAME_NOT_FOUND"
+	ErrInvalidMove       = "INVALID_MOVE"
+	ErrNotHumanTurn      = "NOT_HUMAN_TURN"
+	ErrGameOver          = "GAME_OVER"
+	ErrRateLimitExceeded = "RATE_LIMIT_EXCEEDED"
+	ErrInvalidContent    = "INVALID_CONTENT_TYPE"
+	ErrInvalidRequest    = "INVALID_REQUEST"
+	ErrInvalidFEN        = "INVALID_FEN"
+	ErrInternalError     = "INTERNAL_ERROR"
+)