feat(review): feed impact map into AI-review grounding as additive reference context

[JSONbored]

Grounding-hook slice of #1971: format the computed impact map into an additive prompt section appended to the AI reviewer (like ragContext), so the reviewer reasons about cross-file blast radius. Additive-only, byte-identical when the flag is off or the map is empty — never changes the gate verdict.

Deliverables

• Format the impact map into a pre-rendered 'IMPACT MAP' promptSection consumed via the existing splice point (mirror ragContext handling; GittensoryAiReviewInput src/services/ai-review.ts:135)
• Guard on the resolved review.impact_map flag; absent/empty => no section appended (byte-identical)
• Bounded size to keep the prompt cost-cheap
• Tests: flag-off no section, flag-on section appended, empty-map no section, size cap (branch-counted)

References

• src/services/ai-review.ts:135
• src/review/rag-wire.ts:173
• src/review/grounding-wire.ts

Part of #1971.

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size: S · held for later release (gittensor:feature once activated)

[linear-code]

JSO-2287