fix: clean up OpenCode streams and allow external working directories

Completed OpenCode requests left their event streams open across repeated and
parallel conversations. Each request now closes its own subscription on exit
without cancelling peer sessions, and cancellation preserves its original cause.

Direct-model Execute commands no longer restrict cwd to the workspace. Absolute
paths, parent-relative paths, and symlinks to external directories are accepted.
The workspace remains the default and relative-path base; Ask stays read-only,
and local execution binding, directory validation, and process cleanup remain.

Add real OpenCode lifecycle and real Shell tool-loop regressions, plus matching
feature documentation. Focused checks: 182 passed, 1 skipped; typecheck and lint
passed. Full shared-worktree suite: 3542 passed, 57 skipped, 1 unrelated sidebar
heading failure, reproduced separately and documented.

Release note: 修复 OpenCode 连续及并行对话结束后事件连接未释放的问题；直连模型 Execute 命令现在可直接指定工作区外的绝对路径、相对路径或符号链接目录，Ask 只读边界保持不变。

docs/features/direct-model-agent/ui-design.md

@@ -28,7 +28,7 @@ Job、Subjob 和 Run 继续是内部对象，不创建树形 UI、独立路由
 ```text
 编程能力
   进程执行
-  使用当前工作区和当前用户权限运行 PowerShell/Bash 命令。
+  使用当前用户权限运行 PowerShell、Bash 或 Sh 命令，默认在工作区执行，也可指定其他工作目录。
   编程 Subagent
   将聚焦任务委派给同一模型连接；继承当前工作模式和工作区。
 ```
@@ -54,7 +54,7 @@ PowerShell · packages/app · npm test
 ```
 
 - 命令只显示单行有界摘要，完整参数进入可展开详情。
-- 目录显示工作区相对路径；工作区根显示 `.`。
+- 工作区内目录显示相对路径，工作区根显示 `.`；工作区外目录显示规范化绝对路径。
 - 不在摘要中显示完整环境或凭据。
 
 ### 3.2 状态