v0.5.13 — Provider step (BYO Anthropic vs WPChat Cloud waitlist)

First step in onboarding now asks how you'll pay for the chat. BYO Anthropic key continues the existing flow; WPChat Cloud-waitlist (€10/mo for €5 of tokens, Stripe-billed when it opens) captures optional email signup and skips the API-key + Model steps. Choice persists across re-runs. Cloud service still being built — this ships the UI + early demand signal.