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>

alembic/versions/55b92e155566_add_order_tracking_fields.py

@@ -0,0 +1,31 @@
+"""add_order_tracking_fields
+
+Revision ID: 55b92e155566
+Revises: d2e3f4a5b6c7
+Create Date: 2025-12-20 18:07:51.144136
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '55b92e155566'
+down_revision: Union[str, None] = 'd2e3f4a5b6c7'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # Add new tracking fields to orders table
+    op.add_column('orders', sa.Column('tracking_url', sa.String(length=500), nullable=True))
+    op.add_column('orders', sa.Column('shipment_number', sa.String(length=100), nullable=True))
+    op.add_column('orders', sa.Column('shipping_carrier', sa.String(length=50), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column('orders', 'shipping_carrier')
+    op.drop_column('orders', 'shipment_number')
+    op.drop_column('orders', 'tracking_url')