feat: add customer multiple addresses management

- Add CustomerAddressService with CRUD operations
- Add shop API endpoints for address management (GET, POST, PUT, DELETE)
- Add set default endpoint for address type
- Implement addresses.html with full UI (cards, modals, Alpine.js)
- Integrate saved addresses in checkout flow
  - Address selector dropdowns for shipping/billing
  - Auto-select default addresses
  - Save new address checkbox option
- Add country_iso field alongside country_name
- Add address exceptions (NotFound, LimitExceeded, InvalidType)
- Max 10 addresses per customer limit
- One default address per type (shipping/billing)
- Add unit tests for CustomerAddressService
- Add integration tests for shop addresses API

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models/database/customer.py

@@ -70,7 +70,8 @@ class CustomerAddress(Base, TimestampMixin):
     address_line_2 = Column(String(255))
     city = Column(String(100), nullable=False)
     postal_code = Column(String(20), nullable=False)
-    country = Column(String(100), nullable=False)
+    country_name = Column(String(100), nullable=False)
+    country_iso = Column(String(5), nullable=False)
     is_default = Column(Boolean, default=False)
 
     # Relationships