#269 docs(self-hosting): present GKE and EKS as equal install paths

Summary

The gated /docs/self-hosting overview only offered a GKE install and a GKE-only guided-install prompt. The page now presents two equal install paths.

• The description reads "on Google Cloud (GKE) or AWS (EKS)". The cards are Install on Google Cloud (GKE) and Install on AWS (EKS), plus the setup agent and the Helm chart.
• The setup-agent section links both guided installs and has one copy-able prompt per cloud: selfhost:guided-gke-install and selfhost:guided-eks-install. GUIDED_INSTALL_DOC is replaced by GUIDED_INSTALL_DOCS.
• The architecture diagram is still drawn for GKE. Its caption now says so and lists the AWS equivalents: ALB + ACM, Pod Identity, S3, RDS/Aurora or CloudNativePG. "Previews" in the diagram text becomes "optional".
• Sidebar order: both installs first, then both guided installs.
• No runbook text is added to this repo. A follow-up commit on this PR will regenerate security/selfhost-runbook-fingerprints.json from the relay-agent merge sha.

Companion: AgentWorkforce/relay-agent#102. No Cloud change is needed: /cloud/api/v1/me/selfhost-docs accepts any [a-z0-9-] doc name, and the MCP passes requests through to relay-agent.

Test plan

• npm run typecheck, npm run lint
• vitest run lib/test/selfhost-docs-page.test.tsx lib/test/selfhost-docs.test.ts (22 pass; the new asserts cover both prompts and all four links)
• Fingerprints regenerated from the relay-agent #102 merge sha

Agent-Session: helm-chief coordinator, Claude Code session 091f15c3-697e-4629-aa61-2c8f83eb94d9

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