REF: Add missing import in ssh_backend.rs

- Imported `HashMap` from `std::collections` for future use, ensuring functionality requirements are met.

Author: HansenBerlin

src/app/ssh_backend.rs

@@ -1,3 +1,4 @@
+use std::collections::HashMap;
 use std::path::Path;
 
 use anyhow::{Context, Result};