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>

app/exceptions/__init__.py

@@ -6,6 +6,13 @@ This module provides frontend-friendly exceptions with consistent error codes,
 messages, and HTTP status mappings.
 """
 
+# Address exceptions
+from .address import (
+    AddressLimitExceededException,
+    AddressNotFoundException,
+    InvalidAddressTypeException,
+)
+
 # Admin exceptions
 from .admin import (
     AdminOperationException,