fix(security): validate session name in delete-session to prevent directory deletion (#4583)

* fix(security): validate session name in delete-session to prevent directory deletion

When delete-session receives a path instead of a session name (e.g., due to
shell alias misconfiguration), PathBuf::join() replaces the cache directory
base path entirely, causing remove_dir_all() to delete the user's directory.

Add validate_session_name() to reject names containing '/' or invalid values.

* refactor: use Result instead of Option for validate_session_name

Change validate_session_name to return Result<(), &'static str> instead
of Option<&'static str> for clearer error semantics.

* refactor: use String for validate_session_name errors

Return Result<(), String> and include the session name in error messages
for better debugging context.

* chore: lint changed files

0 files changed, 0 insertions, 0 deletions