feat: SearXNG 搜索集成 + DevTools Docker + PG 备份 + 文档更新

- web_search 工具/插件接入自托管 SearXNG，支持百度/必应/搜狗/360搜索
- DevTools 加入 docker-compose.dev.yml，devtools/Dockerfile
- scripts/pg-backup.sh 数据库备份恢复脚本，docs/pg-backup-migration.md
- 后台思考 + datetime 插件时区默认 Asia/Shanghai
- docker-compose 对齐 volume 名称，清理 tool-engine 残留引用
- README.md / Deploy.md 更新至当前架构（移除简报/tool-engine，新增搜索/跨端同步/DevTools）

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

backend/ai-core/cmd/main.go

@@ -178,7 +178,12 @@ func main() {
 		registerPluginTools(toolRegistry, &pluginJSON.JSONPlugin{})
 		registerPluginTools(toolRegistry, pluginFile.NewFilePlugin(dataDir))
 		registerPluginTools(toolRegistry, pluginHTTP.NewHTTPPlugin())
-		registerPluginTools(toolRegistry, pluginWS.NewWebSearchPlugin())
+		searxngURL := getEnv("SEARXNG_URL", "")
+		if searxngURL != "" {
+			registerPluginTools(toolRegistry, pluginWS.NewWebSearchPluginWithURL(searxngURL))
+		} else {
+			registerPluginTools(toolRegistry, pluginWS.NewWebSearchPlugin())
+		}
 		registerPluginTools(toolRegistry, pluginWF.NewWebFetchPlugin())
 
 		// ai-core 专属工具 — 通过 sdk.Tool 适配器注册