Is your feature request related to a problem? Please describe.
Operators need a quick parity view without downloading full reports.

Describe the solution you'd like

• GET /v1/reconciliation/summary?tenantId&periodStart&periodEnd returns: per-metric {local, stripe, drift_abs, drift_pct}, and overall summary.

Acceptance Criteria

• Works against local compose; JSON example in Swagger.
• Relates to existing /v1/reconciliation/:period route; doesn't replace it.