Follow-up https://github.com/zed-industries/zed/pull/55153
Fixes
https://github.com/zed-industries/zed/discussions/54553#discussioncomment-17091833

When a repository stores its Git data in `~/work/zed/.bare`, creating a
linked worktree from Zed is broken in two visible ways:

- Zed creates `random-code` at:
```
~/work/worktrees/.bare/random-code/.bare
```
instead of:
```
~/work/worktrees/zed/random-code/zed
```

- Because the checkout ends in `.bare`, Zed displays `.bare` as its
worktree name in the title bar, worktree picker, and agent thread
sidebar. Every worktree Zed creates from that repository gets the same
`.bare` label instead of its generated name.

This problem is specific to the path Zed creates. Worktrees using either
of these layouts are not malformed:
```
~/work/worktrees/zed/random-code/zed
~/work/zed/some-worktree
```

https://github.com/zed-industries/zed/pull/55153 introduced repository
identities for bare repositories. This PR uses that identity in the
remaining worktree naming and creation paths.

There are three repository layouts to account for:

- In a normal repository, the common Git directory is `~/work/zed/.git`,
so Zed derives the main worktree at `~/work/zed`. Existing behavior
remains unchanged.

- With `~/work/zed/.bare`, Git has no main worktree. A checkout named
main is still a linked worktree. Zed now treats `~/work/zed` as the
repository identity, creates new worktrees under `~/work/worktrees/zed`,
and displays their generated names.

- With a bare repository named `~/work/foo.git`, `foo.git` is the
repository identity. Its worktree path remains
`~/work/worktrees/foo.git/random-code/foo.git`. Zed uses foo.git to
derive the worktree name random-code, while displaying the repository
itself as foo.

Existing malformed worktrees such as
`~/work/worktrees/.bare/random-code/.bare` are not moved and may
continue to display `.bare`.

Broken:

<p>
<img width="238" height="58" alt="image"
src="https://github.com/user-attachments/assets/1504e4d0-c34a-471f-8e76-c5ec062b1d77"
/>
</p>
<p>
<img width="274" height="49" alt="image"
src="https://github.com/user-attachments/assets/13266ca9-4e64-426c-b03c-e23c924a3597"
/>
</p>
<p>
<img width="574" height="85" alt="image"
src="https://github.com/user-attachments/assets/0fca58c7-5be7-4d36-9067-066d0b80caf8"
/>
</p>

Release Notes:

- Fixed linked worktree names and creation paths for bare Git
repositories.