feat: 插件-工具合并 — 创建 pkg/plugins 共享模块并移除 tool-engine

- 新增 backend/pkg/plugins/ 共享模块：SDK 接口、PluginManager、ToolRegistry（含环形缓冲区调用日志）
- 13 个通用插件从 plugin-manager 迁移至共享模块（import 路径统一）
- ai-core 切换至共享 ToolRegistry，进程内执行（零网络开销），包装 6 个专属工具
- plugin-manager 迁移至共享模块，保留管理 REST API
- 新增 DevTools 插件管理面板（侧边栏 → 🔌 插件管理）
- 移除 tool-engine 服务（从 go.work、DevTools 配置、编译系统）
- 工具调用记录 API 从 Tool-Engine 迁至 AI-Core（/api/v1/tools/calls）
- ai-core ContextStore 启动时从 PostgreSQL 恢复会话历史
- 清理所有过时引用和备份文件

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/plugin-manager/internal/handler/plugin_handler.go

@@ -5,7 +5,7 @@ import (
 	"net/http"
 	"strings"
 
-	"github.com/yourname/cyrene-ai/plugin-manager/internal/manager"
+	"github.com/yourname/cyrene-ai/pkg/plugins/manager"
 )
 
 // PluginHandler exposes the Plugin Manager REST API via net/http.
@@ -39,13 +39,11 @@ func (h *PluginHandler) listPlugins(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *PluginHandler) pluginRoute(w http.ResponseWriter, r *http.Request) {
-	// Path: /api/v1/plugins/{id}[/enable|/disable|/reload|/tools]
 	path := strings.TrimPrefix(r.URL.Path, "/api/v1/plugins/")
 	parts := strings.SplitN(path, "/", 2)
 	pluginID := parts[0]
 
 	if pluginID == "" {
-		// GET /api/v1/plugins (handled by listPlugins normally)
 		h.listPlugins(w, r)
 		return
 	}
@@ -163,7 +161,6 @@ func (h *PluginHandler) toolRoute(w http.ResponseWriter, r *http.Request) {
 	path := strings.TrimPrefix(r.URL.Path, "/api/v1/tools/")
 	toolID := path
 
-	// Check if this is an execute call
 	if strings.HasSuffix(path, "/execute") {
 		toolID = strings.TrimSuffix(path, "/execute")
 		if r.Method != "POST" {