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>

models/database/marketplace_product.py

@@ -6,6 +6,10 @@ Amazon, eBay, CodesWholesale, etc.) in a universal format. It supports:
 - Multi-language translations (via MarketplaceProductTranslation)
 - Flexible attributes for marketplace-specific data
 - Google Shopping fields for Letzshop compatibility
+
+Money values are stored as integer cents (e.g., €105.91 = 10591).
+Weight is stored as integer grams (e.g., 1.5kg = 1500g).
+See docs/architecture/money-handling.md for details.
 """
 
 from enum import Enum
@@ -13,7 +17,6 @@ from enum import Enum
 from sqlalchemy import (
     Boolean,
     Column,
-    Float,
     Index,
     Integer,
     String,
@@ -22,6 +25,7 @@ from sqlalchemy.dialects.sqlite import JSON
 from sqlalchemy.orm import relationship
 
 from app.core.database import Base
+from app.utils.money import cents_to_euros, euros_to_cents
 from models.database.base import TimestampMixin
 
 
@@ -49,6 +53,9 @@ class MarketplaceProduct(Base, TimestampMixin):
 
     This table stores normalized product information from all marketplace sources.
     Localized content (title, description) is stored in MarketplaceProductTranslation.
+
+    Price fields use integer cents for precision (€19.99 = 1999 cents).
+    Weight uses integer grams (1.5kg = 1500 grams).
     """
 
     __tablename__ = "marketplace_products"
@@ -86,11 +93,11 @@ class MarketplaceProduct(Base, TimestampMixin):
     category_path = Column(String)  # Normalized category hierarchy
     condition = Column(String)
 
-    # === PRICING ===
+    # === PRICING (stored as integer cents) ===
     price = Column(String)  # Raw price string "19.99 EUR" (kept for reference)
-    price_numeric = Column(Float)  # Parsed numeric price
+    price_cents = Column(Integer)  # Parsed numeric price in cents
     sale_price = Column(String)  # Raw sale price string
-    sale_price_numeric = Column(Float)  # Parsed numeric sale price
+    sale_price_cents = Column(Integer)  # Parsed numeric sale price in cents
     currency = Column(String(3), default="EUR")
 
     # === MEDIA ===
@@ -102,8 +109,8 @@ class MarketplaceProduct(Base, TimestampMixin):
     attributes = Column(JSON)  # {color, size, material, etc.}
 
     # === PHYSICAL PRODUCT FIELDS ===
-    weight = Column(Float)  # In kg
-    weight_unit = Column(String(10), default="kg")
+    weight_grams = Column(Integer)  # Weight in grams (1.5kg = 1500)
+    weight_unit = Column(String(10), default="kg")  # Display unit
     dimensions = Column(JSON)  # {length, width, height, unit}
 
     # === GOOGLE SHOPPING FIELDS (Preserved for Letzshop) ===
@@ -159,6 +166,44 @@ class MarketplaceProduct(Base, TimestampMixin):
             f"vendor='{self.vendor_name}')>"
         )
 
+    # === PRICE PROPERTIES (Euro convenience accessors) ===
+
+    @property
+    def price_numeric(self) -> float | None:
+        """Get price in euros (for API/display). Legacy name for compatibility."""
+        if self.price_cents is not None:
+            return cents_to_euros(self.price_cents)
+        return None
+
+    @price_numeric.setter
+    def price_numeric(self, value: float | None):
+        """Set price from euros. Legacy name for compatibility."""
+        self.price_cents = euros_to_cents(value) if value is not None else None
+
+    @property
+    def sale_price_numeric(self) -> float | None:
+        """Get sale price in euros (for API/display). Legacy name for compatibility."""
+        if self.sale_price_cents is not None:
+            return cents_to_euros(self.sale_price_cents)
+        return None
+
+    @sale_price_numeric.setter
+    def sale_price_numeric(self, value: float | None):
+        """Set sale price from euros. Legacy name for compatibility."""
+        self.sale_price_cents = euros_to_cents(value) if value is not None else None
+
+    @property
+    def weight(self) -> float | None:
+        """Get weight in kg (for API/display)."""
+        if self.weight_grams is not None:
+            return self.weight_grams / 1000.0
+        return None
+
+    @weight.setter
+    def weight(self, value: float | None):
+        """Set weight from kg."""
+        self.weight_grams = int(value * 1000) if value is not None else None
+
     # === HELPER PROPERTIES ===
 
     @property
@@ -228,12 +273,12 @@ class MarketplaceProduct(Base, TimestampMixin):
 
     @property
     def effective_price(self) -> float | None:
-        """Get the effective numeric price."""
+        """Get the effective numeric price in euros."""
         return self.price_numeric
 
     @property
     def effective_sale_price(self) -> float | None:
-        """Get the effective numeric sale price."""
+        """Get the effective numeric sale price in euros."""
         return self.sale_price_numeric
 
     @property