Title herdr's terminal window like tmux did

tmux set the outer terminal title from `set-titles-string '#h:#W'`, which
is what Hyprland reads for the group bar label. herdr had no equivalent,
so grouped terminals kept whatever the shell or ssh last set - most
visibly wrong when connected to a remote machine.

herdr now renders `ui.window_title` on the server, so mirror the tmux
line. herdr's own default matches, but setting it here keeps the group
bar correct regardless of what upstream picks as its default.

config/herdr/config.toml

@@ -88,3 +88,8 @@ mouse_capture = true
 
 # status-right had the zoom flag followed by #h
 tab_bar_right = [{ type = "zoom" }, { type = "hostname" }]
+
+# set -g set-titles on / set -g set-titles-string '#h:#W', where tmux's #W was
+# the basename of the pane cwd. This is what Hyprland shows in the group bar,
+# and it resolves on the server so remote sessions name the remote host.
+window_title = "{hostname}: {workspace}"