claudetool: improve codereview
Do a bunch of un-vibecoding and bug fixing.
Unfortunately, lots left.
Get rid of vet; gopls check covers it.
Add testing infrastructure and a bunch of fixtures.
diff --git a/claudetool/testdata/no_tests.txtar b/claudetool/testdata/no_tests.txtar
new file mode 100644
index 0000000..ceeb2a5
--- /dev/null
+++ b/claudetool/testdata/no_tests.txtar
@@ -0,0 +1,19 @@
+Going from no tests to no tests is not a regression
+
+-- p.go --
+package p
+
+-- .commit --
+Initial commit
+
+-- other.go --
+package p
+
+func F() {
+}
+
+-- .commit --
+Add func
+
+-- .run_test --
+OK