test(selfhost): add beta smoke matrix and release checklist

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Parent: #1936

Problem

Before letting other teams test the self-host stack, we need a repeatable beta smoke matrix that proves the shipped image works across the supported modes without depending on local maintainer assumptions.

Requirements

• Smoke direct GitHub App mode.
• Smoke telemetry export without brokered token mode.
• Smoke air-gapped/no-telemetry mode.
• Smoke Claude Code-only, Codex-only, and both-provider configurations where credentials are available.
• Smoke SQLite trial mode and document Postgres production mode.
• Smoke Redis cache enabled and Qdrant RAG optional/enabled paths.

Deliverables

• A beta release checklist in docs or a maintained issue template/runbook.
• Portable smoke commands from the repo root or image-first environment.
• Expected metrics/log events for a healthy startup.
• Known warnings that are acceptable in beta versus warnings that block release.

Acceptance criteria

• Maintainer can run through the checklist before publishing the RC image.
• The checklist catches missing secrets, broken compose profiles, bad AI provider config, missing cache, and broken telemetry export.
• The resulting release notes can honestly say which modes were validated.

Expected outcome

The beta image is not just built; it has a repeatable readiness signal that makes external testing credible.

[linear-code]

JSO-2029