feat: add external knowledge retrieval and cross-project activity

Connect Dify, FastGPT and RAGFlow through read-only bindings, encrypted local credentials, shared retrieval and persistent citations. Configuration and removal affect GoodBuddy only.

Show active conversations across projects, retain older live work, and improve project dialog scrolling. Queue concurrent questions and route managed SSH OpenCode questions through the Agent. Preserve recoverable read/search errors and partial search results.

Document the Electron UI automation standard, real model and external knowledge validation, and remaining acceptance limits.

Validation: earlier full regression passed 4081 tests with 66 skipped; subsequent focused remote-question checks and real Linux evidence are recorded in feature progress. Precommit typecheck and lint passed; latest project dialog and shared UI suites passed 58 tests. The full suite was not rerun for the final dialog changes.

Release note: Use external knowledge in conversations, find active work across projects, and answer concurrent local or managed SSH OpenCode questions. Managed SSH questions require the updated Agent adapter.

docs/features/knowledge-base/ui-design.md

@@ -8,6 +8,10 @@
 
 ## 2. 信息架构
 
+当前列表同时容纳本地库与外部绑定，页面增加“管理外部实例”和来源筛选。以下详情结构、
+资料导入和索引状态适用于本地库；外部创建、配置、检索测试及引用的当前实现与待验收项见
+[外部知识库 UI 设计](./external-knowledge-ui-design.md)。
+
 ```text
 知识库
 ├─ 知识库列表
@@ -23,9 +27,9 @@
 
 ## 3. 首次使用
 
-没有知识库时，页面空状态显示唯一的“新建知识库”主操作。创建表单默认只展示名称和
-描述；存储方式与知识图谱放入折叠的“高级设置”。创建完成后进入“文档与来源”，用户
-可以导入文件、文件夹或 URL。
+没有知识库时，页面空状态显示“新建知识库”主操作。创建时先选择类型；本地类型默认
+展示名称和描述，存储方式与知识图谱放入折叠的“高级设置”。本地库创建完成后进入
+“文档与来源”，用户可以导入文件、文件夹或 URL。
 
 文档处理完成后，标题区“用于当前对话”可用。该操作把当前知识库加入当前
 Conversation 的检索范围，返回对话并聚焦输入框。