### Summary 

Follow up on: https://github.com/zed-industries/zed/pull/53550

Threads in the sidebar are now filtered by remote connection in addition
to path list. Previously, two different machines with the same absolute
project paths (e.g. both at `/home/user/project`) would have their
threads merged into a single sidebar group. Now each remote host gets
its own group.

To support this, this PR introduces `RemoteConnectionIdentity`, a
normalized subset of `RemoteConnectionOptions` that includes only the
fields relevant for identity matching (e.g. SSH host + username + port,
but not nickname or connection timeout). All remote host comparisons in
the sidebar, thread metadata store, and workspace persistence now go
through `same_remote_connection_identity()` instead of raw `==` on
`RemoteConnectionOptions`.

#### Follow Up on remoting for sidebar

1. Make the neighbor in archive thread fallback to the main git worktree
instead of the next thread
2. Start implementing remote git operations that archive feature depends
on
3. Make remote connection pool equality use `RemoteConnectionIdentity`

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>