refactor: enforce IOStreams output helpers over direct fmt.Fprint calls

Adds a forbidigo rule requiring fmt.Fprint/Fprintf/Fprintln/Fscan* calls in internal/commands to go through IOStreams (LogInfo/LogInfof/LogError/LogErrorf) instead of writing to stdout/stderr directly, matching the existing json.Marshal convention. The rule is scoped to internal/commands via path-except so it doesn't flag legitimate io.Writer uses elsewhere (doc generation, debug transport, tests).

Converts the resulting violations across the command tree, adding //nolint:forbidigo where the writer genuinely isn't stdout/stderr.