September AI model refresh

The model picker now includes:

• OpenAI GPT 6 Luna, Sol, and Astra, including Pro variants
• Anthropic Opus 5.5 and Fable 5.1
• DeepSeek V4.1 Flash
• Google Gemini 3.8 Flash
• Qwen 3.8 Max 0902 and 3.8 Omni Flash
• xAI Grok 4.7
• Xiaomi MiMo V2.6 Flash, Pro, and Pro UltraSpeed
• Z.ai GLM 5.3 FlashX

GPT 6 Luna is now the default when no model has been selected.