feat: stabilize KYC, international assets and multi-currency schema

- Split mother's name in KYC (last/first)
- Added mileage_unit and fuel_type to Assets
- Expanded AssetCost for international VAT and original currency
- Fixed SQLAlchemy IndexError in asset catalog lookup
- Added exchange_rate and ratings tables to models

backend/app/db/base.py

@@ -1,10 +1,6 @@
-from sqlalchemy.ext.asyncio import AsyncAttrs
-from sqlalchemy.orm import DeclarativeBase
-
-
-class Base(AsyncAttrs, DeclarativeBase):
-    """
-    Base class for all SQLAlchemy models.
-    Includes AsyncAttrs to support async attribute access (lazy loading).
-    """
-    pass
+from app.db.base_class import Base  # noqa
+from app.models.address import Address, GeoPostalCode, GeoStreet, GeoStreetType  # noqa
+from app.models.identity import User, Person, VerificationToken, Wallet  # noqa
+from app.models.organization import Organization, OrganizationMember  # noqa
+from app.models.asset import Asset, AssetCatalog, AssetCost, AssetEvent  # noqa
+from app.models.gamification import UserStats, PointsLedger  # noqa