Base Analytic Product Category Categorization

This module extends analytic accounting entries (account.analytic.line) with a new "Product Category" field. The value is taken automatically from the product used on the line, so users do not have to fill it in manually; it is stored and read-only.

Where it appears: - On the analytic entry form, the Product Category field is shown right after the Product field. - In the analytic entries search view, the same field is available for filtering, and a new "Product Category" filter lets you group entries by product category.

Business behaviour: - The category is derived from the product's category (product_id.categ_id) and saved on the entry. - When the module is installed on an existing database, a pre-installation step fills the new field for all existing analytic lines, so historical data is ready to use without a long manual update.

This touches the analytic accounting area and the product category model (product.category). No new menus, buttons, reports, emails or scheduled jobs are added by the code.