feat(notifications): gate-outcomes section for the maintainer recap (blocked / overridden / false-positive)

[JSONbored]

Digest content section (#1963 'gate outcomes'): summarize the gate's window — how many PRs the gate blocked, how many maintainers overrode, and the blocked-then-merged false-positive count — straight from the GatePrecisionReport already aggregated by services/gate-precision.ts (the same source src/review/ops-wire.ts:10-11 reads). Pure section builder; no new queries.

Deliverables

• buildGateOutcomesRecapSection(report) producing blocked / overridden / false-positive counts + a rate line
• Guard the divide-by-zero / null-rate arm exactly as ops-wire nulls the rate below MIN_SAMPLE (src/review/ops-wire.ts:44) — test both the enough-samples and too-few-samples branches
• Unit test: populated report, empty report, and the null-rate branch (97% branch-counted)

References

• src/review/ops-wire.ts:10
• src/review/ops-wire.ts:44
• src/services/gate-precision.ts

Part of #1963.

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

[linear-code]

JSO-2343