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>

app/api/v1/admin/order_item_exceptions.py

@@ -69,7 +69,7 @@ def list_exceptions(
         limit=limit,
     )
 
-    # Enrich with order info
+    # Enrich with order and vendor info
     response_items = []
     for exc in exceptions:
         item = OrderItemExceptionResponse.model_validate(exc)
@@ -79,6 +79,9 @@ def list_exceptions(
             item.order_id = order.id
             item.order_date = order.order_date
             item.order_status = order.status
+            # Add vendor name for cross-vendor view
+            if order.vendor:
+                item.vendor_name = order.vendor.name
         response_items.append(item)
 
     return OrderItemExceptionListResponse(