Fix self/parent/static error messages to match PHP wording

Change "Cannot use X in the global scope" to "Cannot use X when no
class scope is active" to match PHP's exact error message format.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MagicalTux

core/compiler/compile-classref.go

@@ -819,16 +819,16 @@ func (r *runClassNameOf) Run(ctx phpv.Context) (*phpv.ZVal, error) {
 			}
 			cls := ctx.Class()
 			if cls == nil {
-				return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"self\" in the global scope")
+				return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"self\" when no class scope is active")
 			}
 			return phpv.ZString(cls.GetName()).ZVal(), nil
 		case "parent":
 			cls := ctx.Class()
 			if cls == nil {
 				if ctx.Func() == nil {
-					return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"parent\" in the global scope")
+					return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"parent\" when no class scope is active")
 				}
-				return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"parent\" in the global scope")
+				return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"parent\" when no class scope is active")
 			}
 			parent := cls.GetParent()
 			if parent == nil {
@@ -854,9 +854,9 @@ func (r *runClassNameOf) Run(ctx phpv.Context) (*phpv.ZVal, error) {
 			cls := ctx.Class()
 			if cls == nil {
 				if ctx.Func() == nil {
-					return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"static\" in the global scope")
+					return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"static\" when no class scope is active")
 				}
-				return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"static\" in the global scope")
+				return nil, phpobj.ThrowError(ctx, phpobj.Error, "Cannot use \"static\" when no class scope is active")
 			}
 			return phpv.ZString(cls.GetName()).ZVal(), nil
 		}