Improve(interface): replace some struct with interface for testing (#994)

* fix(trader): get peakPnlPct using posKey
* fix(docs): keep readme at the same page
* improve(interface): replace with interface
* refactor mcp
---------
Co-authored-by: zbhan <zbhan@freewheel.tv>

mcp/interface.go

@@ -0,0 +1,12 @@
+package mcp
+
+import "net/http"
+
+// AIClient AI客户端接口
+type AIClient interface {
+	SetAPIKey(apiKey string, customURL string, customModel string)
+	// CallWithMessages 使用 system + user prompt 调用AI API
+	CallWithMessages(systemPrompt, userPrompt string) (string, error)
+
+	setAuthHeader(reqHeaders http.Header)
+}