Wire RAG + review-grounding (modules ported) + Vectorize/index infra

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Part of #983.

Context

The RAG and review-grounding capability MODULES are ALREADY natively ported on local convergence branches (src/review/{rag,review-grounding}) — this issue is about WIRING them into gittensory's review path and adding the infra they need, NOT re-porting them. review-grounding feeds FINISHED CI results + FULL post-change file content into the reviewer prompt (the #350 / #967 fix: kills hallucinated-CI and undefined-symbol false blockers; flags ciGrounding/fullFileContext). RAG embeds repo code into Vectorize (bge-m3/1024-dim), lazily ensureRepoIndexed on review, with a resumable index_repo queue job + freshness re-index on stale base SHAs. gittensory has ZERO RAG today and no Vectorize binding — that binding (the deferred infra) is added in #1017.

Deliverables

• Wire the ported src/review/review-grounding into the review path so non-frontier reviewers receive finished CI results + full post-change file content; surface ciGrounding/fullFileContext flags.
• Wire the ported src/review/rag codebase RAG into the review path: lazy ensureRepoIndexed on review, fail-safe to NO-context when Vectorize is absent.
• Add the Vectorize binding (coordinated with Infra bindings + adapters (LOCK DO, Vectorize, R2, Browser, private-config home, queue) #1017) + the index_repo queue job (resumable) and the repo-index cron/freshness re-index for stale base SHAs (the deferred index infra).
• Confirm RAG is fail-open: a Vectorize/embeddings failure degrades to no-context review, never blocks or errors the gate.
• Add tests: grounding injects real CI + file content; RAG returns neighbours when indexed and no-context when not.

Acceptance criteria

• Review prompts include finished CI results + full post-change files (grounding) and codebase neighbours (RAG) when available.
• Absent/failed Vectorize degrades gracefully to no-context; the gate verdict is never affected by a RAG failure.
• The repo index lazily builds on review and refreshes on stale base SHAs.

Notes

• Milestone: M1
• Depends on: Infra bindings + adapters (LOCK DO, Vectorize, R2, Browser, private-config home, queue) #1017
• The modules are ALREADY ported (convergence/port-batch + convergence/integrate branches); scope here is wiring + the Vectorize/index-queue/cron infra.
• High-rebase-collision risk: codex churns processors.ts, comments.ts, and signals/engine.ts across other gittensory worktrees. Keep convergence edits minimal + flag-gated and rebase onto main before in-flight codex PRs touching those files settle.