Add Mistral GLM 5.3 model support

I need GLM 5.3 by Mistral added as an AI model option for the chatbot. This model is hosted entirely in the EU and competes with top-tier models from OpenAI and Anthropic in terms of quality, but it's much cheaper. For my Shopify clients who need frontier-level reasoning combined with strict EU data residency (especially for custom-made premium products or complex B2B services), the standard Mistral models aren't strong or reliable enough. GLM 5.3 would be a true frontier-quality option that stays in the EU, making Boei much more appealing for European, privacy-conscious businesses.