feat(review): 'review effort: N/5 (~M min)' line in the unified comment, config-gated

[JSONbored]

Render a compact review effort: N/5 (~M min) line in the unified review comment from the effort estimator, display gated by a review.effort_score manifest toggle (default off). Render + toggle only; depends on the estimator slice.

Deliverables

• Add a single deterministic line to renderUnifiedReviewComment (src/review/unified-comment.ts:479) built from estimateReviewEffort
• Gate display behind a review.effort_score manifest toggle (default off), resolved like other review.* toggles
• Omit the line when toggle off (comment byte-identical to today)
• Tests: toggle on → line present with band+minutes, toggle off → omitted (both branches)

References

• src/review/unified-comment.ts:479
• part of #1955

Part of #1955.

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size: XS · held for later release (gittensor:bug once activated)

[linear-code]

JSO-2254