[REF] product_origin_char: simplify to template-based origin

- Move origin_text field from product.supplierinfo to product.template
- Add related field in product.product for variant access
- Remove dependency on product_main_seller
- Update views to show field near category (editable)
- Rewrite tests for new architecture
- Update all documentation (README, readme/ fragments)
- Bump version to 18.0.2.0.0

product_origin_char/readme/USAGE.rst

@@ -1,26 +1,18 @@
 **To add origin information to a product:**
 
 #. Go to a product form
-#. Open the **Purchase** tab
-#. In the **Vendors** section, select a supplier line
-#. Fill in the **Origin** field with free-form text describing the origin
-   (e.g., "Valencia, Huerta de..., Spain")
+#. Find the **Origin** field (near the product category)
+#. Fill in the origin with free-form text
+   (e.g., "Valencia, Spain", "Local producer - Basque Country")
 #. Save the product
 
-**To view origin information:**
+**To view origin information in lists:**
 
-* The **Origin** field will be automatically displayed on the product form
-  (below the **Main Vendor** field in the Purchase tab)
-* The origin shown is from the **main vendor** (first supplier in the list)
-* You can also add the Origin column to product list views
+* In product list views, enable the optional "Origin" column
+* The origin is shown for both product templates and variants
 
-**To change the displayed origin:**
+**Product variants:**
 
-* Reorder the vendors list to change which is the main vendor
-* The origin text will automatically update to show the new main vendor's origin
-
-**Multi-language support:**
-
-* The origin text is translatable
-* Switch to another language and edit the supplier info to provide a translation
-* Each language can have a different description of the origin
+* All variants of a product template share the same origin
+* Updating the origin on any variant updates the template
+* This ensures consistency across all variants