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/tenancy/services/admin_service.py

@@ -802,6 +802,14 @@ class AdminService:
         """
         return db.query(User).filter(User.id == user_id).first()
 
+    def get_user_by_email(self, db: Session, email: str) -> User | None:
+        """Get user by email."""
+        return db.query(User).filter(User.email == email).first()
+
+    def get_user_by_username(self, db: Session, username: str) -> User | None:
+        """Get user by username."""
+        return db.query(User).filter(User.username == username).first()
+
     def _get_user_by_id_or_raise(self, db: Session, user_id: int) -> User:
         """Get user by ID or raise UserNotFoundException."""
         user = db.query(User).filter(User.id == user_id).first()
@@ -871,5 +879,40 @@ class AdminService:
         db.add_all(roles)
 
 
+    def get_user_statistics(self, db: Session) -> dict:
+        """
+        Get user statistics for dashboards.
+
+        Returns:
+            Dict with total_users, active_users, inactive_users, admin_users, activation_rate
+        """
+        from sqlalchemy import func
+
+        total_users = db.query(func.count(User.id)).scalar() or 0
+        active_users = (
+            db.query(func.count(User.id))
+            .filter(User.is_active == True)  # noqa: E712
+            .scalar()
+            or 0
+        )
+        inactive_users = total_users - active_users
+        admin_users = (
+            db.query(func.count(User.id))
+            .filter(User.role.in_(["super_admin", "platform_admin"]))
+            .scalar()
+            or 0
+        )
+
+        return {
+            "total_users": total_users,
+            "active_users": active_users,
+            "inactive_users": inactive_users,
+            "admin_users": admin_users,
+            "activation_rate": (
+                (active_users / total_users * 100) if total_users > 0 else 0
+            ),
+        }
+
+
 # Create service instance
 admin_service = AdminService()