feat(loyalty): Phase 7 — advanced analytics (cohort, churn, revenue)

New analytics_service.py with three analytics features:

- Cohort retention: groups cards by enrollment month, tracks % with
  any transaction in each subsequent month. Returns matrix suitable
  for Chart.js heatmap. GET /analytics/cohorts?months_back=6
- Churn detection: flags cards as "at risk" when inactive > 2x their
  average inter-transaction interval (default 60d for new cards).
  Returns ranked list. GET /analytics/churn?limit=50
- Revenue attribution: monthly and per-store aggregation of point-
  earning transactions. GET /analytics/revenue?months_back=6

Endpoints added to both admin API (/admin/loyalty/merchants/{id}/
analytics/*) and store API (/store/loyalty/analytics/*) so merchants
can see their own analytics.

342 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/loyalty/routes/api/store.py

@@ -198,6 +198,51 @@ def get_merchant_stats(
     return MerchantStatsResponse(**stats)
 
 
+@router.get("/analytics/cohorts")
+def get_cohort_retention(
+    months_back: int = Query(6, ge=1, le=24),
+    current_user: User = Depends(get_current_store_api),
+    db: Session = Depends(get_db),
+):
+    """Cohort retention matrix for this merchant's loyalty program."""
+    from app.modules.loyalty.services.analytics_service import analytics_service
+
+    merchant_id = get_store_merchant_id(db, current_user.token_store_id)
+    return analytics_service.get_cohort_retention(
+        db, merchant_id, months_back=months_back
+    )
+
+
+@router.get("/analytics/churn")
+def get_at_risk_cards(
+    limit: int = Query(50, ge=1, le=200),
+    current_user: User = Depends(get_current_store_api),
+    db: Session = Depends(get_db),
+):
+    """Cards at risk of churn for this merchant."""
+    from app.modules.loyalty.services.analytics_service import analytics_service
+
+    merchant_id = get_store_merchant_id(db, current_user.token_store_id)
+    return analytics_service.get_at_risk_cards(
+        db, merchant_id, limit=limit
+    )
+
+
+@router.get("/analytics/revenue")
+def get_revenue_attribution(
+    months_back: int = Query(6, ge=1, le=24),
+    current_user: User = Depends(get_current_store_api),
+    db: Session = Depends(get_db),
+):
+    """Revenue attribution from loyalty transactions."""
+    from app.modules.loyalty.services.analytics_service import analytics_service
+
+    merchant_id = get_store_merchant_id(db, current_user.token_store_id)
+    return analytics_service.get_revenue_attribution(
+        db, merchant_id, months_back=months_back
+    )
+
+
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