[ADD] product_origin_char: Free text origin field per supplier

New addon to replace structured country/state fields with flexible
free-text origin descriptions.

Features:
- Translatable origin_text field in product.supplierinfo
- Computed origin field in products based on main_seller_id
- Support for creative supplier origin descriptions
- Full OCA documentation structure
- ES/EU translations included
- 8 unit tests (all passing)

Replaces product_origin for use cases where suppliers use non-standardized
origin descriptions (e.g., 'Valencia, Spain', 'Huerta de...', etc.)

Depends on: product, product_main_seller
Author: Criptomart
Funding: Elika Bilbo

product_origin_char/readme/USAGE.rst

@@ -0,0 +1,26 @@
+**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")
+#. Save the product
+
+**To view origin information:**
+
+* 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
+
+**To change the displayed origin:**
+
+* 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