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,

app/exceptions/address.py

@@ -0,0 +1,38 @@
+# app/exceptions/address.py
+"""
+Address-related custom exceptions.
+
+Used for customer address management operations.
+"""
+
+from .base import BusinessLogicException, ResourceNotFoundException
+
+
+class AddressNotFoundException(ResourceNotFoundException):
+    """Raised when a customer address is not found."""
+
+    def __init__(self, address_id: str | int):
+        super().__init__(
+            resource_type="Address",
+            identifier=str(address_id),
+        )
+
+
+class AddressLimitExceededException(BusinessLogicException):
+    """Raised when customer exceeds maximum number of addresses."""
+
+    def __init__(self, max_addresses: int = 10):
+        super().__init__(
+            message=f"Maximum number of addresses ({max_addresses}) reached",
+            error_code="ADDRESS_LIMIT_EXCEEDED",
+        )
+
+
+class InvalidAddressTypeException(BusinessLogicException):
+    """Raised when an invalid address type is provided."""
+
+    def __init__(self, address_type: str):
+        super().__init__(
+            message=f"Invalid address type '{address_type}'. Must be 'shipping' or 'billing'",
+            error_code="INVALID_ADDRESS_TYPE",
+        )