feat(notifications): calibration / reversal-rate section for the maintainer recap

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Digest content section (#1963 'calibration'): surface the ground-truth accuracy signal — auto-actions reverted by humans and the reversal rate — reusing the Calibration / reversal shapes defined at src/review/ops.ts:61 and the reversalRate field at src/review/alerts.ts:56. Pure section builder over the RecapReport; conveys 'is the gate calibrated' without any raw score/reward internals.

Deliverables

• buildCalibrationRecapSection(report) emitting reversals + reversalRate + a plain-English note (mirror the detectAnomalies calibration-drift phrasing at src/review/alerts.ts:175)
• Handle the 'nothing auto-acted' branch (reversalRate 0 when merged+closed is 0) — test both arms
• Unit test: drift-present, healthy, and zero-denominator cases

References

• src/review/ops.ts:61
• src/review/alerts.ts:56
• src/review/alerts.ts:175

Part of #1963.

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

[linear-code]

JSO-2344