claudetool: tweak bashkit error message when changing branches

- remove reference to outie (normal sketch sessions
  don't have the concept introduced in the prompt anywhere)
- tweak wording for precision
- add some extra details
- point out the Push button
- let claude rewrite a bit for concision
diff --git a/claudetool/bashkit/bashkit_test.go b/claudetool/bashkit/bashkit_test.go
index ee40582..0c86550 100644
--- a/claudetool/bashkit/bashkit_test.go
+++ b/claudetool/bashkit/bashkit_test.go
@@ -299,7 +299,7 @@
 			name:        "git branch rename sketch-wip",
 			script:      "git branch -m sketch-wip new-branch",
 			wantErr:     true,
-			errMatch:    "changing the 'sketch-wip' branch is not allowed",
+			errMatch:    "cannot leave 'sketch-wip' branch",
 			resetBefore: true,
 		},
 		{