feat: add Avian as LLM provider

[avianion]

Summary

Register Avian model IDs and provider metadata so the codebase recognizes avian/* as valid model names.

Changes

• Add avian/deepseek-v3.2, avian/kimi-k2.5, avian/glm-5, avian/minimax-m2.5 to the ModelName type (both copies)
• Add avian to ALLOWED_MODEL_PREFIXES
• Add avianModels constant, spread into models and providerModelNames
• Add avian entry to providerDomains and getLogoForModel

What this does NOT include

This PR only adds type/constant registration. The actual provider module (avian.ts), env var (AVIAN_API_KEY), and chat completions routing are not included and would need to be added in a follow-up PR for these models to actually work end-to-end.

Models

Model	Notes
avian/deepseek-v3.2	DeepSeek V3 (0324)
avian/kimi-k2.5	Moonshot Kimi K2.5
avian/glm-5	Zhipu GLM-5
avian/minimax-m2.5	MiniMax M2.5