[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/CREDITS.rst

@@ -0,0 +1,9 @@
+**Development:**
+
+* `Criptomart <https://criptomart.net>`_
+
+**Funding:**
+
+* `Elika Bilbo <https://elikabilbo.eus>`_
+
+This module was developed by Criptomart with funding from Elika Bilbo.