config: prefer machine-local /etc/wldash/config.yml when present

On a shared (NFS-roamed) home, ~/.config/wldash/config.yml is identical on
every machine. Prefer a host-specific /etc/wldash/config.yml when it exists so
each machine can keep its own layout without conflicting; --config still
overrides both. Enables the 'factor host-specific config to /etc' pattern for
shared-home fleets.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main.rs

@@ -47,7 +47,8 @@ usage: wldash [OPTIONS]
 
 OPTIONS:
   --config CONFIG_FILE                     use the specified config file
-                                           (~/.config/wldash/config.yml by default)
+                                           (/etc/wldash/config.yml if present,
+                                           else ~/.config/wldash/config.yml)
   --write-default-config [v1|v2|toplevel]  generate and write a new config file
                                            (v2 by default)
   --desktop-refresh                        refresh desktop file cache
@@ -69,6 +70,18 @@ fn create_required_directories() {
     ensure_dir_exists(&dir_cache_wldash);
 }
 
+/// Default config path. On a shared (e.g. NFS-roamed) home, a host-specific
+/// config at /etc/wldash/config.yml takes precedence over the roamed
+/// ~/.config/wldash/config.yml, so each machine can keep its own layout
+/// without conflicting. An explicit --config still overrides both.
+fn default_config_file() -> String {
+    let etc = "/etc/wldash/config.yml";
+    if Path::new(etc).exists() {
+        return etc.to_string();
+    }
+    format!("{}/wldash/config.yml", xdg::config_folder())
+}
+
 fn main() {
     let mut args = env::args();
     // Skip program name
@@ -76,7 +89,7 @@ fn main() {
 
     create_required_directories();
 
-    let mut config_file = format!("{}/wldash/config.yml", xdg::config_folder());
+    let mut config_file = default_config_file();
 
     loop {
         match args.next() {