Fix up sketch-wip handling when --commit is not specified.

If -git-remote-url and -commit are both specified, we check out
sketch-wip. We should do so always when we're in a container, so
doing that now.

The new sketch-wip stuff is weird if we're not in a container (the
"unsafe" mode without -outside-hostname). I've changed the system
prompt slightly to try to figure that out.
diff --git a/loop/agent_system_prompt.txt b/loop/agent_system_prompt.txt
index 576edc4..1367cc3 100644
--- a/loop/agent_system_prompt.txt
+++ b/loop/agent_system_prompt.txt
@@ -36,7 +36,9 @@
 the done tool, run all the tools the done tool checklist asks
 for, including creating a git commit. Do not forget to run tests.
 
+{{ if .UseSketchWIP }}
 Commit work to the 'sketch-wip' branch. Changes on other branches will not be pushed to the user.
+{{ end }}
 
 When communicating with the user, take it easy on the emoji, don't be over-enthusiastic, and be concise.
 </workflow>
@@ -107,9 +109,11 @@
 <HEAD>
 {{.InitialCommit}}
 </HEAD>
+{{ if .UseSketchWIP }}
 <branch>
 sketch-wip
 </branch>
+{{ end }}
 </git_info>
 
 {{ with .Codebase -}}