Rewrite the -count=1 note to match the current files (closes #77)

The note under the canonical Go `make test` example in `prompts/REPO_POLICIES.md` named a cache-busting build argument that `--no-cache` replaced, and said Go's test result cache survived in earlier image layers. Neither is true of the current files.

The note now says where that cache can replay a pass: on a developer's machine, where the Makefile target runs, so both invocations there keep `-count=1`. The `test` phase of the `Dockerfile` has nothing to replay, since its base image holds no result for the repo's tests and no step before `go test` runs one, so it needs no `-count=1`. Go stores only passing results, so neither run can report a stored pass.

Model: opus-5-5

TODO.md

@@ -21,6 +21,12 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-04: Rewrote the note under the canonical Go `make test` example in
+  `REPO_POLICIES.md` (issue 77), which still named the cache-busting build
+  argument that `--no-cache` replaced. It now says where Go's test result cache
+  can replay a pass: on a developer's machine, where the Makefile target runs,
+  and not in the `test` phase of the `Dockerfile`, whose base image and earlier
+  steps hold no result for the repo's tests.
 - 2026-10-04: The Makefile examples in the Go styleguide and the HTTP server
   conventions now fall back to `dev` when `git describe` prints nothing (outside
   a git checkout, or where git is missing or refuses the checkout), instead of