feat(review): render impact map as a compact section in the unified review comment

[JSONbored]

Surface slice of #1971: render a computed impact map as a compact, public-safe section (changed module -> affected modules/callers) in the unified comment. Presentation only, additive, byte-identical when absent/empty. Does NOT feed grounding (that's a separate slice).

Deliverables

• Add optional impactMap to UnifiedReviewInput + a compact renderer (table or collapsible) via the section helper in src/review/unified-comment.ts:449
• Public-safe path escaping; omit section when the map is empty
• Bounded rows (cap displayed affected modules; '+N more')
• Tests: populated map renders, empty = no section, cap/overflow line, escaping (branch-counted)

References

• src/review/unified-comment.ts:473
• src/review/unified-comment.ts:449
• src/review/unified-comment.ts:48

Part of #1971.

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

[linear-code]

JSO-2286