feat(mcp): integrate MCP Server into backend service as built-in endpoint

- Add MCP Controller and register /mcp route
- MCP Server now uses OpenAPI Token for authentication
- Update frontend settings to show built-in MCP endpoint config
- Update docs to reflect integrated MCP endpoint

internal/router/mcp.go

@@ -0,0 +1,20 @@
+package router
+
+import (
+	"github.com/engigu/taskpool/internal/middleware"
+	"github.com/gin-gonic/gin"
+)
+
+// initMCPRoutes 初始化 MCP Server 路由
+// 使用 OpenAPI Token 进行鉴权
+func initMCPRoutes(root *gin.RouterGroup, c *Controllers) {
+	// MCP 路由组 (使用 Bearer Token 鉴权，复用 OpenAPI 中间件)
+	mcp := root.Group("/mcp")
+	mcp.Use(middleware.OpenapiRequired())
+	{
+		// 所有 MCP 请求都通过同一个 handler 处理
+		// StreamableHTTP 协议支持 POST 和 GET
+		mcp.POST("/*action", c.MCP.HandleMCP)
+		mcp.GET("/*action", c.MCP.HandleMCP)
+	}
+}