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/services/letzshop/client_service.py

@@ -116,6 +116,9 @@ query {
                 code
                 provider
             }
+            data {
+                __typename
+            }
         }
     }
 }
@@ -194,6 +197,9 @@ query {
                 code
                 provider
             }
+            data {
+                __typename
+            }
         }
     }
 }
@@ -272,6 +278,9 @@ query GetShipment($id: ID!) {
                 code
                 provider
             }
+            data {
+                __typename
+            }
         }
     }
 }
@@ -349,6 +358,9 @@ query GetShipmentsPaginated($first: Int!, $after: String) {{
                     }}
                 }}
             }}
+            data {{
+                __typename
+            }}
         }}
     }}
 }}