claudetool: add simplified patch support

For weaker models.

Also, improve fallback parsing introduced earlier.
diff --git a/claudetool/patch_test.go b/claudetool/patch_test.go
index 93bbe1c..6a8d090 100644
--- a/claudetool/patch_test.go
+++ b/claudetool/patch_test.go
@@ -320,7 +320,7 @@
 	// Test single patch format (PatchInputOne)
 	inputOne := PatchInputOne{
 		Path: testFile,
-		Patches: PatchRequest{
+		Patches: &PatchRequest{
 			Operation: "overwrite",
 			NewText:   "Single patch format\n",
 		},