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/unit/models/database/test_product.py

@@ -165,16 +165,16 @@ class TestProductModel:
 
     def test_product_reset_to_source(self, db, test_vendor, test_marketplace_product):
         """Test reset_to_source methods."""
-        # Set up marketplace product values
-        test_marketplace_product.price_numeric = 100.00
+        # Set up marketplace product values (use cents internally)
+        test_marketplace_product.price_cents = 10000  # €100.00
         test_marketplace_product.brand = "SourceBrand"
         db.commit()
 
-        # Create product with overrides
+        # Create product with overrides (price property converts euros to cents)
         product = Product(
             vendor_id=test_vendor.id,
             marketplace_product_id=test_marketplace_product.id,
-            price=89.99,
+            price_cents=8999,  # €89.99
             brand="OverrideBrand",
         )
         db.add(product)
@@ -184,13 +184,14 @@ class TestProductModel:
         assert product.effective_price == 89.99
         assert product.effective_brand == "OverrideBrand"
 
-        # Reset price to source
-        product.reset_field_to_source("price")
+        # Reset price_cents to source (OVERRIDABLE_FIELDS now uses _cents names)
+        product.reset_field_to_source("price_cents")
         db.commit()
         db.refresh(product)
 
-        assert product.price is None
-        assert product.effective_price == 100.00  # Now inherits
+        assert product.price_cents is None
+        assert product.price is None  # Property returns None when cents is None
+        assert product.effective_price == 100.00  # Now inherits from marketplace
 
         # Reset all fields
         product.reset_all_to_source()