First run: without an agentlab.yaml, configure and up ask one question — use the detected defaults or customize? — and only Customize runs the form

[teemow]

Part of #119.

Problem

A first agentlab up (or agentlab configure without --defaults) on a terminal runs the whole form — cluster name, users and passwords, components, ports, models — before anything happens. configure --defaults writes the right lab for nearly everyone (the platform with agents, observability and Backstage on; the discovery fills in this machine's free ports and host model servers), but a newcomer does not know the flag and up never offers it: loadOrCreateConfig in main.go goes straight to forms.Run.

Proposed solution

With no agentlab.yaml, on a terminal, both agentlab configure (without --defaults) and every command that creates the config on the way (up foremost — loadOrCreateConfig serves them all) run the discovery and print its report as today, then ask one huh confirm — along the lines of "No agentlab.yaml yet. Use the detected defaults — the agent platform with agents, observability and Backstage, three users, the free ports above — or customize every option?" Affirmative Use the defaults: what configure --defaults does (Validate, Save, the saved-configuration summary configure prints, with agentlab configure named as the way to change it later). Negative Customize: the form, as today.

Unchanged: configure --defaults and the component flags pin without a question; configure on an existing agentlab.yaml runs the form with the current values; off a terminal a missing agentlab.yaml is refused with the configure --defaults pointer — CI and coding agents write the config explicitly, and keep doing so.

The question names the components, so "defaults" means something without opening the docs.

Acceptance criteria

• In an empty directory on a terminal, agentlab up prints the discovery, asks the one question, and after Use the defaults continues into the boot with the canonical lab saved; after Customize the form runs as today.
• agentlab configure without flags in an empty directory asks the same question; with --defaults it asks nothing.
• With stdin not a terminal, a missing agentlab.yaml is refused with the configure --defaults pointer as today.
• A scripted-keystroke test covers both answers.
• docs/getting-started.md's quick start shows agentlab up as the first command and configure as the way to customize.

[marians]

Note for whoever picks this up: the confirm this issue needs already exists, from #136.

• forms.Confirm(title, description, affirmative, negative string, dflt bool) (bool, error) in internal/forms/confirm.go — built through newForm, so the package's test hook drives it with a scripted keystroke stream (see TestConfirmDrive, and drive_test.go's newDriver), and it runs .WithAccessible(forms.Accessible()), which is now the single reader of $ACCESSIBLE (main.go's accessibleMode() delegates to it).
• forms.ErrAborted re-exports huh's user abort, so the Ctrl-C branch needs no huh import.
• internal/lab/prompt.go shows the shape the lab settled on for a question outside configure: onTerminal, askConfirm and the side effect as package vars ("A variable so tests can stand in for …"), a pure decision function for the table test, and — the rule this issue shares — nothing the question does may fail the command that asked it.

Two things #136 learned that apply here directly:

1. In accessible mode the prompt reads lines, so Ctrl-C is a real SIGINT that ends the process. Anything the run has already earned (a written agentlab.yaml, for this issue) must be persisted before the question, not after.
2. loadOrCreateConfig (main.go) is the one place all of up, configure and the rest reach the form through, and its term.IsTerminal(os.Stdin.Fd()) refusal is the headless contract to keep.