Feature: Add support for custom OpenAI-compatible API

This update enables users to configure any OpenAI-compatible API endpoint,
allowing the use of:
- OpenAI official API (GPT-4, GPT-4o, etc.)
- OpenRouter (access to multiple models)
- Local deployed models (Ollama, LM Studio, etc.)
- Other OpenAI-format compatible API services

Changes:
- config: Add custom_api_url, custom_api_key, custom_model_name fields
- mcp: Add SetCustomAPI function and ProviderCustom constant
- trader: Update AI initialization logic to support custom API
- manager: Pass custom API config to trader instances
- Add CUSTOM_API.md documentation with usage examples
- Update config.json.example with custom API sample

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: tinkle-community <tinklefund@gmail.com>

mcp/client.go

@@ -16,6 +16,7 @@ type Provider string
 const (
 	ProviderDeepSeek Provider = "deepseek"
 	ProviderQwen     Provider = "qwen"
+	ProviderCustom   Provider = "custom"
 )
 
 // Config AI API配置
@@ -53,6 +54,15 @@ func SetQwenAPIKey(apiKey, secretKey string) {
 	defaultConfig.Model = "qwen-plus" // 可选: qwen-turbo, qwen-plus, qwen-max
 }
 
+// SetCustomAPI 设置自定义OpenAI兼容API
+func SetCustomAPI(apiURL, apiKey, modelName string) {
+	defaultConfig.Provider = ProviderCustom
+	defaultConfig.APIKey = apiKey
+	defaultConfig.BaseURL = apiURL
+	defaultConfig.Model = modelName
+	defaultConfig.Timeout = 120 * time.Second
+}
+
 // SetConfig 设置完整的AI配置（高级用户）
 func SetConfig(config Config) {
 	if config.Timeout == 0 {