feat(loyalty): refactor analytics into shared template and add merchant stats API

Extract analytics stat cards, points activity, and location breakdown
into a shared partial used by admin, merchant, and store dashboards.
Add merchant stats API endpoint and client-side merchant filter on admin
analytics page. Extend stats schema with new_this_month and
estimated_liability_cents fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -28,6 +28,7 @@ from app.modules.loyalty.schemas import (
     ProgramResponse,
     ProgramUpdate,
 )
+from app.modules.loyalty.schemas.program import MerchantStatsResponse
 from app.modules.loyalty.services import program_service
 from app.modules.tenancy.models import Merchant
 
@@ -49,6 +50,21 @@ def _build_program_response(program) -> ProgramResponse:
     return response
 
 
+# =============================================================================
+# Statistics
+# =============================================================================
+
+
+@router.get("/stats", response_model=MerchantStatsResponse)
+def get_stats(
+    merchant: Merchant = Depends(get_merchant_for_current_user),
+    db: Session = Depends(get_db),
+):
+    """Get merchant-wide loyalty statistics across all locations."""
+    stats = program_service.get_merchant_stats(db, merchant.id)
+    return MerchantStatsResponse(**stats)
+
+
 # =============================================================================
 # Program CRUD
 # =============================================================================