refactor(arch): eliminate all cross-module model imports in service layer

Enforce MOD-025/MOD-026 rules: zero top-level cross-module model imports
remain in any service file. All 66 files migrated using deferred import
patterns (method-body, _get_model() helpers, instance-cached self._Model)
and new cross-module service methods in tenancy. Documentation updated
with Pattern 6 (deferred imports), migration plan marked complete, and
violations status reflects 84→0 service-layer violations.

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

app/modules/customers/services/customer_service.py

@@ -30,7 +30,7 @@ from app.modules.tenancy.exceptions import (
     StoreNotActiveException,
     StoreNotFoundException,
 )
-from app.modules.tenancy.models import Store
+from app.modules.tenancy.services.store_service import store_service as _store_service
 
 logger = logging.getLogger(__name__)
 
@@ -62,7 +62,7 @@ class CustomerService:
             CustomerValidationException: If customer data is invalid
         """
         # Verify store exists and is active
-        store = db.query(Store).filter(Store.id == store_id).first()
+        store = _store_service.get_store_by_id_optional(db, store_id)
         if not store:
             raise StoreNotFoundException(str(store_id), identifier_type="id")
 
@@ -150,7 +150,7 @@ class CustomerService:
             CustomerNotActiveException: If customer account is inactive
         """
         # Verify store exists
-        store = db.query(Store).filter(Store.id == store_id).first()
+        store = _store_service.get_store_by_id_optional(db, store_id)
         if not store:
             raise StoreNotFoundException(str(store_id), identifier_type="id")
 
@@ -575,5 +575,96 @@ class CustomerService:
         return customer
 
 
+    # ========================================================================
+    # Cross-module public API methods
+    # ========================================================================
+
+    def create_customer_for_enrollment(
+        self,
+        db: Session,
+        store_id: int,
+        email: str,
+        first_name: str = "",
+        last_name: str = "",
+        phone: str | None = None,
+    ) -> Customer:
+        """
+        Create a customer for loyalty/external enrollment.
+
+        Creates a customer with an unusable password hash.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+            email: Customer email
+            first_name: First name
+            last_name: Last name
+            phone: Phone number
+
+        Returns:
+            Created Customer object
+        """
+        import secrets
+
+        unusable_hash = f"!enrollment!{secrets.token_hex(32)}"
+        store_code = "STORE"
+        try:
+            from app.modules.tenancy.services.store_service import store_service
+
+            store = store_service.get_store_by_id_optional(db, store_id)
+            if store:
+                store_code = store.store_code
+        except Exception:
+            pass
+
+        cust_number = self._generate_customer_number(db, store_id, store_code)
+        customer = Customer(
+            email=email,
+            first_name=first_name,
+            last_name=last_name,
+            phone=phone,
+            hashed_password=unusable_hash,
+            customer_number=cust_number,
+            store_id=store_id,
+            is_active=True,
+        )
+        db.add(customer)
+        db.flush()
+        return customer
+
+    def get_customer_by_id(self, db: Session, customer_id: int) -> Customer | None:
+        """
+        Get customer by ID without store scope.
+
+        Args:
+            db: Database session
+            customer_id: Customer ID
+
+        Returns:
+            Customer object or None
+        """
+        return db.query(Customer).filter(Customer.id == customer_id).first()
+
+    def get_store_customer_count(self, db: Session, store_id: int) -> int:
+        """
+        Count customers for a store.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+
+        Returns:
+            Customer count
+        """
+        from sqlalchemy import func
+
+        return (
+            db.query(func.count(Customer.id))
+            .filter(Customer.store_id == store_id)
+            .scalar()
+            or 0
+        )
+
+
 # Singleton instance
 customer_service = CustomerService()