[Feature]: Add Swahili (sw) language translations

Description

Bagisto currently ships with 22 locales but no support for Swahili (Kiswahili), spoken by an estimated 150-200 million people across East and Central Africa (Tanzania, Kenya, Uganda, DRC, Rwanda, Burundi) — one of the official languages of the African Union and the most widely spoken language in East Africa, a rapidly growing e-commerce region.

This issue tracks the addition of complete Swahili (sw) translations:

• Root framework files: lang/sw/ (auth, passwords, pagination, validation)
• All 14 packages exposing translation files (Admin, Shop, Installer, Core, Customer, Product, Attribute, DataTransfer, Stripe, PayPal, PayU, PhonePe, Razorpay, PayGlocal)
• Locale registration in SupportedLocales.php
• Installer locale labels (sw / swahili) across all existing locale files

Terminology follows common East African commerce usage (bidhaa, bei, malipo, risiti, kodi, sarafu, duka la mtandaoni). PR to follow.