Deployment doc: recommend cloud over docker, defuse the slug question, offer OpenRouter

[ReganBell]

An agent following the generated deployment.md currently quizzes a first-time operator with questions they can't answer well:

• It can present the docker target as the recommended path (it's the qm init default), when docker is only meant for a quick local test drive. The doc now says to recommend a cloud provider (Fly.io when the operator has no preference) and never present docker as the path for a real deployment.
• It makes the org slug a standalone decision, and operators reasonably wonder whether it must be globally unique. It doesn't — it's a local name used in the package name, resource names, and Slack branding. The doc now says to derive it from the organization's name and confirm it in passing.
• It offers only Anthropic and OpenAI as model providers, though OpenRouter is fully supported (core config OPENROUTER_API_KEY and the Admin key-validation endpoint). The doc now lists all three and notes that "decide later" is fine since the key is entered on the Admin page.

Also glosses the slug the same way in docs/getting-started.md.

🤖 Generated with Claude Code

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[ReganBell]

Also rewrites the sign-in email guidance: the agent now asks what the operator already uses for email instead of presenting a transport menu (SMTP vs Resend, DKIM/SPF). SMTP with an existing account is the recommended default; Resend is for operators who prefer it and control DNS.