feat: add claudecode with oauth to AI providers

backend/internal/ai/provider.go

@@ -27,6 +27,8 @@ func NewProvider(name, apiKey, model, endpoint string) (Provider, error) {
 		return newGemini(apiKey, model), nil
 	case "ollama":
 		return newOllama(endpoint, model), nil
+	case "claudecode":
+		return newClaudeCode(model), nil
 	default:
 		return nil, fmt.Errorf("unknown provider: %s", name)
 	}