Rewrite onboarding docs for a human-free signup path

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Problem: Every existing onboarding lane (miner, maintainer, repo-owner, operator) is entirely manual today — no lane describes a human-free signup experience.

Area: ORB / Docs (apps/loopover-ui/content/docs/, mirroring beta-onboarding.mdx's existing structure; src/services/repo-onboarding-pack.ts/src/signals/onboarding-pack.ts for the existing onboarding-pack data shape to reference).

Proposal: Write documentation for the new self-serve lane once it exists, alongside (not replacing) the existing manual-operator docs.

Deliverables:

• New onboarding documentation for the self-serve hosted path, following the existing beta-onboarding.mdx doc's structure and voice.

Boundaries:

• Do not start until Redesign the setup-wizard for true multi-instance self-serve provisioning #4926 (setup-wizard redesign) and Decouple "admin of a GitHub install" from "has a running container" #4927 (decouple admin-of-install from running container) have actually landed — this documents that flow, it can't be written accurately ahead of it existing. Check both issues' state before picking this up.
• Does not replace or edit the existing manual-operator docs.

Contributor-eligible once #4926/#4927 land — pure docs, no code, no infra/credential access needed. Blocked until then, not ambiguous about what to write once unblocked.

[linear-code]

JSO-3590

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Deferred as a group tonight (2026-07-19): this cluster (#4919, #4920, #4930, #4931, #4932) needs a real billing-provider and pricing-model decision with no engineering-inferable answer, and nothing else in ORB Cloud Readiness is currently blocked on it. Left open, revisit in a dedicated pricing/business session rather than guessed at here. #4920 (the plan/quota/subscription/invoice data model) is the right one to start with whenever that session happens — the other four build on it.