[16.0][ADD] product_catalog_sale_rental: bridge catalog with rental orders

[eantones]

Summary

• New glue module between product_catalog_sale and sale_rental so that products added from the catalog create proper rental lines with rental_type, rental_qty, dates and computed product_uom_qty
• Adds readonly=False to start_date/end_date on sale.order.line to work around a circular dependency issue in sale_start_end_dates computes during programmatic create()
• Includes Catalan and Spanish translations for the module and for the untranslated parent modules (product_catalog, product_catalog_sale)

Test plan

• Install module on a database with product_catalog_sale and sale_rental
• Configure a rental service product with rented_product_id
• Create a sale order with default start/end dates, open catalog, add the rental product — verify line has correct rental_type, rental_qty, dates and product_uom_qty = qty × days
• Increase/decrease quantity via catalog — verify rental_qty and product_uom_qty update
• Remove rental product via catalog (Eliminar) — verify line is deleted
• Add a regular (non-rental) product via catalog — verify no interference (no dates, no rental fields)
• Add a product manually via "Añadir un producto" — verify standard behavior unchanged
• Try adding rental product without dates set on order — verify UserError is shown
• Mixed order: add both rental and regular products from catalog — verify both coexist correctly
• Verify translations appear in Catalan/Spanish UI

[codecov]

Codecov Report

❌ Patch coverage is 27.45098% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.16%. Comparing base (419ffde) to head (65210b7).
⚠️ Report is 7 commits behind head on 16.0.

Files with missing lines	Patch %	Lines
product_catalog_sale_rental/models/sale_order.py	24.48%	37 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             16.0     #868      +/-   ##
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- Coverage   44.30%   44.16%   -0.14%     
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  Files         313      316       +3     
  Lines        6230     6281      +51     
  Branches      989     1000      +11     
==========================================
+ Hits         2760     2774      +14     
- Misses       3449     3486      +37     
  Partials       21       21              

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