claudetool: add simplified patch support

For weaker models.

Also, improve fallback parsing introduced earlier.
diff --git a/loop/agent.go b/loop/agent.go
index 310564d..85a4afe 100644
--- a/loop/agent.go
+++ b/loop/agent.go
@@ -1394,6 +1394,7 @@
 	patchTool := &claudetool.PatchTool{
 		Callback:         a.patchCallback,
 		Pwd:              a.workingDir,
+		Simplified:       llm.UseSimplifiedPatch(a.config.Service),
 		ClipboardEnabled: experiment.Enabled("clipboard"),
 	}