owner-led(visual-agent): optional LLM visual review + verdict

[JSONbored]

Parent roadmap: #525
Parent epic: #577

Owner-led — assigned to @JSONbored.

Goal

Optional LLM visual review + verdict: feed the before/after/diff images + change summary to a reviewer for a short verdict/summary (advisory first, gate-capable later).

Reuse

Either inline Workers AI (metagraphed pattern) or an external private reviewer endpoint (awesome-claude pattern, HMAC-signed).

Scope

• Prompt with images + per-route change %; structured output { verdict, confidence, summary }.
• Advisory by default; optional pass/fail check run later. Fallback to manual-review on error/timeout.

Acceptance

The managed comment includes a concise visual-review summary; failures degrade to advisory/manual-review.

[JSONbored]

Closing as not planned (2026-07-01 issue audit): Optional LLM visual verdict belongs to the converged review engine, not the retired separate worker.