create_session always creates a worktree -- no option for a local/in-place session

**Mood:** 😕
**Category:** Bug

When spinning up a sub-session via the `create_session` tool, there is no parameter to choose a local/in-place (folder-backed) session -- it always creates a git worktree. For read-only workflows like `/m-code-review`, the worktree checkout adds unnecessary filesystem overhead, and there is no way to opt out. The tool exposes `project_id`, `base_branch`, `model`, `reasoning_effort`, `kickoff_*`, `name`, `notify_on_idle`, and `coordinate_with_creator`, but nothing to select session type.

**Expected:** a way to request an in-place/local session (e.g. a `session_type` field or a worktree toggle on `create_session`), with the resulting type reflected back in `get_session`.

---
| Field | Value |
| --- | --- |
| App version | 1.0.60 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /agents |
| Tenure | Month 1 |

首先跟踪 create_session 工具和 get_session 响应，重点关注当前如何选择和报告 worktrees 及会话元数据。定义 session-type 选项，并验证 in-place 会话不会创建 worktree，同时 get_session 会反映生成的类型。

由索引模型根据 Issue 内容生成。