feat: add Avian as a named LLM provider

Add Avian (https://avian.io) as an OpenAI-compatible provider with
API base https://api.avian.io/v1 and AVIAN_API_KEY env var support.

Models: deepseek/deepseek-v3.2, moonshotai/kimi-k2.5, z-ai/glm-5,
minimax/minimax-m2.5. Supports chat completions, streaming, and
function calling.

Changes:
- Add Avian to ProvidersConfig struct, IsEmpty(), HasProvidersConfig()
- Add avian protocol to factory provider and default API base
- Add avian case to legacy provider selection (factory.go)
- Add avian migration rule for old config format
- Add default model entries to ModelList (deepseek-v3.2, kimi-k2.5)
- Add avian to example config
- Update AllProviders test count from 18 to 19

pkg/providers/factory.go

@@ -181,6 +181,15 @@ func resolveProviderSelection(cfg *config.Config) (providerSelection, error) {
 					sel.model = "deepseek-chat"
 				}
 			}
+		case "avian":
+			if cfg.Providers.Avian.APIKey != "" {
+				sel.apiKey = cfg.Providers.Avian.APIKey
+				sel.apiBase = cfg.Providers.Avian.APIBase
+				sel.proxy = cfg.Providers.Avian.Proxy
+				if sel.apiBase == "" {
+					sel.apiBase = "https://api.avian.io/v1"
+				}
+			}
 		case "mistral":
 			if cfg.Providers.Mistral.APIKey != "" {
 				sel.apiKey = cfg.Providers.Mistral.APIKey
@@ -300,6 +309,13 @@ func resolveProviderSelection(cfg *config.Config) (providerSelection, error) {
 			if sel.apiBase == "" {
 				sel.apiBase = "https://api.mistral.ai/v1"
 			}
+		case strings.HasPrefix(model, "avian/") && cfg.Providers.Avian.APIKey != "":
+			sel.apiKey = cfg.Providers.Avian.APIKey
+			sel.apiBase = cfg.Providers.Avian.APIBase
+			sel.proxy = cfg.Providers.Avian.Proxy
+			if sel.apiBase == "" {
+				sel.apiBase = "https://api.avian.io/v1"
+			}
 		case cfg.Providers.VLLM.APIBase != "":
 			sel.apiKey = cfg.Providers.VLLM.APIKey
 			sel.apiBase = cfg.Providers.VLLM.APIBase

pkg/providers/factory_provider.go

@@ -94,7 +94,7 @@ func CreateProviderFromConfig(cfg *config.ModelConfig) (LLMProvider, string, err
 
 	case "litellm", "openrouter", "groq", "zhipu", "gemini", "nvidia",
 		"ollama", "moonshot", "shengsuanyun", "deepseek", "cerebras",
-		"volcengine", "vllm", "qwen", "mistral":
+		"volcengine", "vllm", "qwen", "mistral", "avian":
 		// All other OpenAI-compatible HTTP providers
 		if cfg.APIKey == "" && cfg.APIBase == "" {
 			return nil, "", fmt.Errorf("api_key or api_base is required for HTTP-based protocol %q", protocol)
@@ -208,6 +208,8 @@ func getDefaultAPIBase(protocol string) string {
 		return "http://localhost:8000/v1"
 	case "mistral":
 		return "https://api.mistral.ai/v1"
+	case "avian":
+		return "https://api.avian.io/v1"
 	default:
 		return ""
 	}