Allow opening the FS root dir as a remote project (#30190)

### Todo

* [x] Allow opening `ssh://username@host:/` from the CLI
* [x] Allow selecting `/` in the `open path` picker
* [x] Allow selecting the home directory in the `open path` picker

Release Notes:

- Changed the initial state of the SSH project picker to show the full
path to your home directory on the remote machine, instead of `~`.
- Added the ability to open `/` as a project folder over SSH

---------

Co-authored-by: Agus Zubiaga <hi@aguz.me>

crates/worktree/src/worktree.rs

@@ -2648,7 +2648,7 @@ impl Snapshot {
     }
 
     pub fn root_entry(&self) -> Option<&Entry> {
-        self.entry_for_path("")
+        self.entries_by_path.first()
     }
 
     /// TODO: what's the difference between `root_dir` and `abs_path`?