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>

app/routes/admin_pages.py

@@ -807,6 +807,25 @@ async def admin_vendor_products_page(
     )
 
 
+@router.get("/vendor-products/create", response_class=HTMLResponse, include_in_schema=False)
+async def admin_vendor_product_create_page(
+    request: Request,
+    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    db: Session = Depends(get_db),
+):
+    """
+    Render vendor product create page.
+    Create a new vendor product entry.
+    """
+    return templates.TemplateResponse(
+        "admin/vendor-product-create.html",
+        {
+            "request": request,
+            "user": current_user,
+        },
+    )
+
+
 @router.get(
     "/vendor-products/{product_id}",
     response_class=HTMLResponse,
@@ -832,6 +851,31 @@ async def admin_vendor_product_detail_page(
     )
 
 
+@router.get(
+    "/vendor-products/{product_id}/edit",
+    response_class=HTMLResponse,
+    include_in_schema=False,
+)
+async def admin_vendor_product_edit_page(
+    request: Request,
+    product_id: int = Path(..., description="Vendor Product ID"),
+    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    db: Session = Depends(get_db),
+):
+    """
+    Render vendor product edit page.
+    Edit vendor product information and overrides.
+    """
+    return templates.TemplateResponse(
+        "admin/vendor-product-edit.html",
+        {
+            "request": request,
+            "user": current_user,
+            "product_id": product_id,
+        },
+    )
+
+
 # ============================================================================
 # SETTINGS ROUTES
 # ============================================================================