Make script/test fail on flaky failures and enable -race (closes #32)

script/test ended with a verbose rerun whose exit status became the
script's, so a test that failed once and passed on the retry gave a
green build. It now follows the REPO_POLICIES.md pattern: go vet, then
go test -count=1 -timeout 30s -race -cover; on failure a verbose rerun
for the details, then exit 1. -count=1 stays on both go test lines
because the Dockerfile keeps Go's build cache between builds.

The tests that gave the secret binary a minute, and the PGP unlocker
test's 30-second timer, now use 10 seconds, so a hang fails with the
test's own message before the package's 30-second timeout. The README
describes the new run.

Model: opus-5-5

internal/secret/pgpunlock_test.go

@@ -317,8 +317,8 @@ func testCreatePGPUnlocker(
 	t.Helper()
 
 	// Set a limited test timeout to avoid hanging
-	timer := time.AfterFunc(30*time.Second, func() {
-		t.Fatalf("Test timed out after 30 seconds")
+	timer := time.AfterFunc(10*time.Second, func() {
+		t.Fatalf("Test timed out after 10 seconds")
 	})
 	defer timer.Stop()