fix(template): children were red because ./... cannot see the entrypoint

Closes #1. Closes #2.

A repo generated from this template failed `task check` on errcheck from its
first commit, while the template's own `task check` was green. The reason is
not in the code:

    Go ignores directories whose names begin with "_" or "." when expanding
    package patterns like ./...

The entrypoint lives in cmd/__PROJECT_NAME__. So `go build ./...`,
`go vet ./...`, `go test ./...` and `golangci-lint run ./...` ALL silently
skip the one package every generated repo is built around:

    $ go list ./...
    __MODULE_PATH__/internal/agent
    __MODULE_PATH__/pkg/litellm        <- no cmd package

After substitution the directory has a real name, becomes visible, and the
defect appears. Template green, children red, by construction -- and invisible
to anyone reading either repo's CI.

Fixes the one live defect: `defer shutdown(ctx)` dropped an error, and
SetupTelemetry returns func(context.Context) error.

Two of the three defects these issues describe were already fixed and neither
issue knew: go.sum has been committed for some time, and resp.Body.Close is
already wrapped. Verified before touching anything rather than trusted from
the issue text.

Adds scripts/tests/generated-child_test.sh, wired into `task check`: it
substitutes the tracked tree into a throwaway child and gates go list / build
/ vet / golangci-lint on the RESULT. Without it the next entrypoint defect
rots exactly the same way.

Not done by adding ./cmd/__PROJECT_NAME__ to the lint command, which does work
-- naming a path directly bypasses the pattern exclusion -- because it reports
a gofumpt violation on the import block that does not exist in any child. The
formatter's import grouping depends on the module path and the template's is a
placeholder, so that route turns the gate red over an artifact of being a
template.

The harness reads tracked files from the working tree rather than
`git archive HEAD`: it runs inside `task check`, so it must gate what is about
to be committed. Archiving HEAD reported a stale pass against an unstaged fix
on first use here.

Proven to fail when it should: red on the unfixed entrypoint, and red again on
the stale-HEAD read, before going green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

cmd/__PROJECT_NAME__/main.go

@@ -22,7 +22,13 @@ func main() {
 		fmt.Fprintf(os.Stderr, "telemetry: %v\n", err)
 		os.Exit(1)
 	}
-	defer shutdown(ctx)
+	// Wrapped rather than bare: errcheck flags a deferred call that drops an
+	// error, and SetupTelemetry returns func(context.Context) error. The bare
+	// form shipped for months because this package lives in a directory whose
+	// name starts with an underscore, which Go's ./... expansion skips -- so
+	// the template's own lint never saw it while every generated repo, where
+	// the directory has a real name, inherited the failure.
+	defer func() { _ = shutdown(ctx) }()
 
 	llm := litellm.New(
 		env("LITELLM_MODEL", "berget/llama-3.3-70b"),