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/pages/merchant.py

@@ -145,24 +145,13 @@ async def merchant_loyalty_analytics(
     """
     Render merchant loyalty analytics page.
 
-    Shows aggregate loyalty program stats across all merchant stores.
+    Stats are loaded client-side via JS fetch.
     """
-    merchant_id = merchant.id
-    stats = {}
-    try:
-        stats = program_service.get_merchant_stats(db, merchant_id)
-    except Exception:
-        logger.warning(
-            f"Failed to load loyalty stats for merchant {merchant_id}",
-            exc_info=True,
-        )
-
     context = _get_merchant_context(
         request,
         db,
         current_user,
-        loyalty_stats=stats,
-        merchant_id=merchant_id,
+        merchant_id=merchant.id,
     )
     return templates.TemplateResponse(
         "loyalty/merchant/analytics.html",