Add native Settings and complete live configuration reload

Add compact branded Settings with safe atomic edits, external config refresh and a draggable sidebar. Reconcile services, update connected displays and input devices, apply live layout policy and window rules, and resolve initial floating placement before tiled insertion. Package the Settings launcher and shared Ferese icon.

compositor/src/main.rs

@@ -43,6 +43,19 @@ use crate::config::Config;
 fn main() -> Result<(), Box<dyn Error>> {
     init_logging();
 
+    // Settings validates a candidate before atomically replacing the user's file.
+    // This mode never opens a display, input device, or compositor socket.
+    let args = std::env::args_os().skip(1).collect::<Vec<_>>();
+    if args.first().is_some_and(|arg| arg == "--check-config") {
+        if args.len() != 2 {
+            return Err("usage: ferese --check-config PATH".into());
+        }
+        let source = std::fs::read_to_string(&args[1])?;
+        Config::parse_source(&source)?.runtime_config()?;
+        println!("Configuration is valid");
+        return Ok(());
+    }
+
     let launch = LaunchConfig::from_environment()
         .map_err(|error| io::Error::new(io::ErrorKind::InvalidInput, error))?;
     let initial_source = config::config_path().and_then(|path| std::fs::read_to_string(path).ok());