fix(cli): keep enable's internal warnings out of the terminal; humanize decode failures

enable never called logging.Init, so ladder warnings fell back to slog's stderr default and leaked ogen's full decoder chain into the flow's output (seen live when a gateway 502 failed the mirror offer). Init logging to .entire/logs after the bootstrap block, so a declined bootstrap leaves no stray .entire/ behind.

renderCoreError now collapses undecodable responses (gateway error pages — no typed error exists on that path) to one line: 'the control plane returned HTTP 502 — try again shortly' instead of the raw wrap chain. Applies to every control-plane command.