fix(loyalty): cross-store enrollment, card scoping, i18n flicker

Fix duplicate card creation when the same email enrolls at different
stores under the same merchant, and implement cross-location-aware
enrollment behavior.

- Cross-location enabled (default): one card per customer per merchant.
  Re-enrolling at another store returns the existing card with a
  "works at all our locations" message + store list.
- Cross-location disabled: one card per customer per store. Enrolling
  at a different store creates a separate card for that store.

Changes:
- Migration loyalty_004: replace (merchant_id, customer_id) unique
  index with (enrolled_at_store_id, customer_id). Per-merchant
  uniqueness enforced at application layer when cross-location enabled.
- card_service.resolve_customer_id: cross-store email lookup via
  merchant_id param to find existing cardholders at other stores.
- card_service.enroll_customer: branch duplicate check on
  allow_cross_location_redemption setting.
- card_service.search_card_for_store: cross-store email search when
  cross-location enabled so staff at store2 can find cards from store1.
- card_service.get_card_by_customer_and_store: new service method.
- storefront enrollment: catch LoyaltyCardAlreadyExistsException,
  return existing card with already_enrolled flag, locations, and
  cross-location context. Server-rendered i18n via Jinja2 tojson.
- enroll-success.html: conditional cross-store/single-store messaging,
  server-rendered translations and context, i18n_modules block added.
- dashboard.html, history.html: replace $t() with server-side _() to
  fix i18n flicker across all storefront templates.
- Fix device-mobile icon → phone icon.
- 4 new i18n keys in 4 locales (en, fr, de, lb).
- Docs: updated data-model, business-logic, production-launch-plan,
  user-journeys with cross-location behavior and E2E test checklist.
- 12 new unit tests + 3 new integration tests (334 total pass).

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

app/modules/loyalty/routes/pages/storefront.py

@@ -133,6 +133,7 @@ async def loyalty_self_enrollment(
 async def loyalty_enrollment_success(
     request: Request,
     card: str = Query(None, description="Card number"),
+    already: str = Query(None, description="Already enrolled flag"),
     db: Session = Depends(get_db),
 ):
     """
@@ -149,6 +150,27 @@ async def loyalty_enrollment_success(
 
     context = get_storefront_context(request, db=db)
     context["enrolled_card_number"] = card
+
+    # Provide merchant locations and cross-location flag server-side so
+    # the template doesn't depend on sessionStorage surviving refreshes.
+    store = getattr(request.state, "store", None)
+    if store:
+        from app.modules.loyalty.services import program_service
+
+        settings = program_service.get_merchant_settings(db, store.merchant_id)
+        locations = program_service.get_merchant_locations(db, store.merchant_id)
+        context["server_already_enrolled"] = already == "1"
+        context["server_allow_cross_location"] = (
+            settings.allow_cross_location_redemption if settings else True
+        )
+        context["server_merchant_locations"] = [
+            {"id": loc.id, "name": loc.name} for loc in locations
+        ]
+    else:
+        context["server_already_enrolled"] = False
+        context["server_allow_cross_location"] = True
+        context["server_merchant_locations"] = []
+
     return templates.TemplateResponse(
         "loyalty/storefront/enroll-success.html",
         context,