List partner-allowed products with price breakdown

Return the products this partner may order, each with its full price breakdown so the partner can render an itemized cart. Devices are one-time and expose a line-by-line breakdown (what the customer pays for); the membership is recurring and exposes pricing per billing cycle plus a split_per_cycle (server vs SIM). Prices are net (excl. VAT); VAT is applied at order time.

Names and breakdown labels are localized via the lang query parameter (or the Accept-Language header): cs, de, en, es, et, fi, fr, lt, lv, nl, pt — anything else falls back to English. The chosen language is echoed as lang.