feat: integer cents money handling, order page fixes, and vendor filter persistence

Money Handling Architecture:
- Store all monetary values as integer cents (€105.91 = 10591)
- Add app/utils/money.py with Money class and conversion helpers
- Add static/shared/js/money.js for frontend formatting
- Update all database models to use _cents columns (Product, Order, etc.)
- Update CSV processor to convert prices to cents on import
- Add Alembic migration for Float to Integer conversion
- Create .architecture-rules/money.yaml with 7 validation rules
- Add docs/architecture/money-handling.md documentation

Order Details Page Fixes:
- Fix customer name showing 'undefined undefined' - use flat field names
- Fix vendor info empty - add vendor_name/vendor_code to OrderDetailResponse
- Fix shipping address using wrong nested object structure
- Enrich order detail API response with vendor info

Vendor Filter Persistence Fixes:
- Fix orders.js: restoreSavedVendor now sets selectedVendor and filters
- Fix orders.js: init() only loads orders if no saved vendor to restore
- Fix marketplace-letzshop.js: restoreSavedVendor calls selectVendor()
- Fix marketplace-letzshop.js: clearVendorSelection clears TomSelect dropdown
- Align vendor selector placeholder text between pages

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

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

tests/fixtures/customer_fixtures.py

@@ -53,19 +53,60 @@ def test_customer_address(db, test_vendor, test_customer):
 
 @pytest.fixture
 def test_order(db, test_vendor, test_customer, test_customer_address):
-    """Create a test order."""
+    """Create a test order with customer/address snapshots."""
+    from datetime import datetime, timezone
+
     order = Order(
         vendor_id=test_vendor.id,
         customer_id=test_customer.id,
         order_number="TEST-ORD-001",
         status="pending",
+        channel="direct",
         subtotal=99.99,
         total_amount=99.99,
         currency="EUR",
-        shipping_address_id=test_customer_address.id,
-        billing_address_id=test_customer_address.id,
+        order_date=datetime.now(timezone.utc),
+        # Customer snapshot
+        customer_first_name=test_customer.first_name,
+        customer_last_name=test_customer.last_name,
+        customer_email=test_customer.email,
+        customer_phone=None,
+        # Shipping address snapshot
+        ship_first_name=test_customer_address.first_name,
+        ship_last_name=test_customer_address.last_name,
+        ship_address_line_1=test_customer_address.address_line_1,
+        ship_city=test_customer_address.city,
+        ship_postal_code=test_customer_address.postal_code,
+        ship_country_iso="LU",
+        # Billing address snapshot
+        bill_first_name=test_customer_address.first_name,
+        bill_last_name=test_customer_address.last_name,
+        bill_address_line_1=test_customer_address.address_line_1,
+        bill_city=test_customer_address.city,
+        bill_postal_code=test_customer_address.postal_code,
+        bill_country_iso="LU",
     )
     db.add(order)
     db.commit()
     db.refresh(order)
     return order
+
+
+@pytest.fixture
+def test_order_item(db, test_order, test_product):
+    """Create a test order item."""
+    from models.database.order import OrderItem
+
+    order_item = OrderItem(
+        order_id=test_order.id,
+        product_id=test_product.id,
+        product_name="Test Product",
+        product_sku="TEST-SKU-001",
+        quantity=1,
+        unit_price=49.99,
+        total_price=49.99,
+    )
+    db.add(order_item)
+    db.commit()
+    db.refresh(order_item)
+    return order_item