feat: add Create Product and CRUD actions to vendor-products page

- Add "Create Product" button in header
- Update actions column to View, Edit, Delete
- Add create/edit pages with forms and vendor selector
- Add POST/PATCH API endpoints for vendor products
- Add create_product and update_product service methods

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models/schema/vendor_product.py

@@ -21,12 +21,14 @@ class VendorProductListItem(BaseModel):
     vendor_id: int
     vendor_name: str | None = None
     vendor_code: str | None = None
-    marketplace_product_id: int
+    marketplace_product_id: int | None = None
     vendor_sku: str | None = None
     title: str | None = None
     brand: str | None = None
     price: float | None = None
     currency: str | None = None
+    effective_price: float | None = None
+    effective_currency: str | None = None
     is_active: bool | None = None
     is_featured: bool | None = None
     is_digital: bool | None = None
@@ -142,3 +144,43 @@ class RemoveProductResponse(BaseModel):
     """Response from product removal."""
 
     message: str
+
+
+class VendorProductCreate(BaseModel):
+    """Schema for creating a vendor product."""
+
+    vendor_id: int
+    title: str
+    brand: str | None = None
+    vendor_sku: str | None = None
+    gtin: str | None = None
+    price: float | None = None
+    currency: str = "EUR"
+    availability: str | None = None
+    is_active: bool = True
+    is_featured: bool = False
+    is_digital: bool = False
+    description: str | None = None
+
+
+class VendorProductUpdate(BaseModel):
+    """Schema for updating a vendor product."""
+
+    title: str | None = None
+    brand: str | None = None
+    vendor_sku: str | None = None
+    gtin: str | None = None
+    price_override: float | None = None
+    currency_override: str | None = None
+    availability: str | None = None
+    is_active: bool | None = None
+    is_featured: bool | None = None
+    is_digital: bool | None = None
+    description: str | None = None
+
+
+class VendorProductCreateResponse(BaseModel):
+    """Response from product creation."""
+
+    id: int
+    message: str