fix(plugins): 内置清单终审 15 → 13 —— kbtree/multimodal 翻案加回

## 翻案依据（逐方法对照公开 SDK，非方法名 grep）

初判把 kbtree/multimodal 归入"只用公开 SDK"，错了。两边的
s.Knowledge() / s.LLM() **同名但接口面不同**：

- kbtree 需要 KnowledgeAPI.Subtree/CategoryCounts/SearchIn/Categories
  与 KnowledgeTreeView/KnowledgeCategoryCount 类型 —— 公开 KnowledgeAPI
  只有 Search/Add/List，树视图类型公开面根本没有
- multimodal 需要 LLMAPI.Chat + LLMMessage/LLMContentBlock ——
  公开 LLMAPI 只有 ListSources/SetSource/CurrentSource，没有 Chat

外置它们 = OCR/看图/转写、知识树浏览静默失效。

## 最终内置 13 个

  cli webui agentcli healthcheck pluginmgr seq remotedevice
  clawhubadapter kbtree multimodal cfgmgr skillmgr seemedia

外置 5 个（SDK 仓 example/ 已提供工程并已部署验证）：
  cmd localuse mcp（本轮）+ ai_image files（此前）+ timer（更早）

## 文档同步（中英 6 份）

数量 11 → 13；判定标准小节补「终审翻案」与教训：
**判外置与否必须逐方法对照公开接口，同名方法不等于同面。**

验证：go build/vet/test 全绿；生产实例已部署新内核 + 新插件包，
四个按需插件经 plugin_start 拉起、工具全部注册（cmd_run /
local_screensee / mcp_* / files_edit_line 实核）。

assets/docs/en/OVERVIEW.md

@@ -100,7 +100,7 @@ Code is in the project root, implemented in Go.
 
 Core functionality is operational. Plugin system and SDK are ready for independent external plugin development.
 
-- Built-in plugins (11): webui / cli / agentcli / cfgmgr / healthcheck / pluginmgr / clawhubadapter / remotedevice / skillmgr / seemedia / seq
+- Built-in plugins (13): webui / cli / agentcli / cfgmgr / healthcheck / kbtree / multimodal / pluginmgr / clawhubadapter / remotedevice / skillmgr / seemedia / seq
 - Criterion: **a plugin stays built-in only if it requires internal-SDK-only capabilities**; everything else ships as an .hmap external plugin (see ARCHITECTURE)
 - External plugin examples ([homeagent-sdk](https://github.com/JianFeeeee/homeagentsdk) repo `example/`, both Go and Lua types): qq / files / a2a / ai_image / bili / browser / calendar / editdoc / memo / music / ocr / rss / sanitizer / weather / luademo
 - Distribution: `.hmap` plugin package format, installable via WebUI