docs: 项目概览(OVERVIEW.md) + 插件开发指南(PLUGIN_DEV.md) + MCP 适配器插件

- OVERVIEW.md: 非技术用户友好的项目介绍和目标
- PLUGIN_DEV.md: 完整插件开发指南（含三种开发方式、API 参考、最佳实践）
- internal/plugins/mcp/: MCP 协议适配器插件（JSON-RPC over stdio/SSE）
  - client.go: MCP 客户端（ListTools / CallTool）
  - stdio.go: 子进程 stdin/stdout 传输
  - sse.go: HTTP POST 传输
  - plugin.go: init() 自注册 + Settings 配置读取
- README.md 更新链接

internal/plugins/mcp/plugin.go

@@ -0,0 +1,147 @@
+package mcp
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"sync"
+
+	"gitcode.com/JianFeeeee/HomeAgent/internal/plugin"
+	sdk "gitcode.com/JianFeeeee/HomeAgent/internal/sdk"
+)
+
+// MCP 服务器配置（来自 config_mcp 表或 skill.json）
+type serverConfig struct {
+	Name    string   `json:"name"`
+	Command string   `json:"command,omitempty"`  // stdio 模式
+	Args    []string `json:"args,omitempty"`
+	Env     []string `json:"env,omitempty"`
+	URL     string   `json:"url,omitempty"`      // SSE 模式
+}
+
+func init() {
+	plugin.RegisterFactory("mcp", func(name string, config map[string]interface{}) (sdk.Plugin, error) {
+		return New(name), nil
+	})
+}
+
+type Plugin struct {
+	name    string
+	servers []*Server
+	mu      sync.Mutex
+	wg      sync.WaitGroup
+}
+
+func New(name string) *Plugin {
+	return &Plugin{name: name}
+}
+
+func (p *Plugin) Name() string { return p.name }
+
+func (p *Plugin) Start(s *sdk.PluginSDK) error {
+	// 从插件配置读取 MCP 服务器列表
+	cfgs, err := p.loadConfig(s)
+	if err != nil {
+		return fmt.Errorf("load mcp config: %w", err)
+	}
+	if len(cfgs) == 0 {
+		log.Printf("[mcp] no servers configured, idle")
+		return nil
+	}
+
+	for _, cfg := range cfgs {
+		server, tools, err := p.connectServer(cfg)
+		if err != nil {
+			log.Printf("[mcp] connect %s: %v", cfg.Name, err)
+			continue
+		}
+
+		for _, tool := range tools {
+			toolName := fmt.Sprintf("%s_%s", cfg.Name, tool.Name)
+			tDef := sdk.ToolDef{
+				Name:        toolName,
+				Description: fmt.Sprintf("[MCP/%s] %s", cfg.Name, tool.Description),
+				Parameters:  tool.InputSchema,
+			}
+			tHandler := p.makeHandler(server, tool.Name)
+			if err := s.RegisterTool(toolName, tDef, tHandler); err != nil {
+				log.Printf("[mcp] register tool %s: %v", toolName, err)
+				continue
+			}
+			log.Printf("[mcp] registered tool: %s (%s)", toolName, cfg.Name)
+		}
+
+		p.mu.Lock()
+		p.servers = append(p.servers, server)
+		p.mu.Unlock()
+		log.Printf("[mcp] connected server: %s (%d tools)", cfg.Name, len(tools))
+	}
+
+	return nil
+}
+
+func (p *Plugin) loadConfig(s *sdk.PluginSDK) ([]serverConfig, error) {
+	// 优先从 skill.json（config map）读取
+	raw, err := s.Settings().Get("servers")
+	if err == nil {
+		switch v := raw.(type) {
+		case string:
+			var cfgs []serverConfig
+			if err := json.Unmarshal([]byte(v), &cfgs); err == nil && len(cfgs) > 0 {
+				return cfgs, nil
+			}
+		case []interface{}:
+			data, _ := json.Marshal(v)
+			var cfgs []serverConfig
+			if json.Unmarshal(data, &cfgs) == nil && len(cfgs) > 0 {
+				return cfgs, nil
+			}
+		}
+	}
+
+	// 备用：从 JSON 文件读取
+	// 没有配置时不报错，只返回空
+	return nil, nil
+}
+
+func (p *Plugin) connectServer(cfg serverConfig) (*Server, []MCPTool, error) {
+	var transport Transport
+
+	if cfg.URL != "" {
+		transport = NewSSETransport(cfg.URL)
+	} else if cfg.Command != "" {
+		var err error
+		transport, err = NewStdioTransport(cfg.Command, cfg.Args, cfg.Env)
+		if err != nil {
+			return nil, nil, fmt.Errorf("stdio transport: %w", err)
+		}
+	} else {
+		return nil, nil, fmt.Errorf("neither command nor url specified")
+	}
+
+	server := NewServer(cfg.Name, transport)
+
+	tools, err := server.ListTools()
+	if err != nil {
+		transport.Close()
+		return nil, nil, fmt.Errorf("list tools: %w", err)
+	}
+
+	return server, tools, nil
+}
+
+func (p *Plugin) makeHandler(server *Server, toolName string) sdk.ToolHandler {
+	return func(args map[string]interface{}) (interface{}, error) {
+		return server.CallTool(toolName, args)
+	}
+}
+
+func (p *Plugin) Stop() error {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	for _, s := range p.servers {
+		s.Close()
+	}
+	p.servers = nil
+	return nil
+}