Add caps lock indicator and keyboard layout support

- Add caps lock ring color change when caps lock is enabled (matching swaylock-effects)
- Add configurable caps lock colors: ring, text, key highlight, backspace highlight
- Add show_caps_lock_text config option (enabled by default)
- Add keyboard layout display with show_keyboard_layout option (disabled by default)
- Change keyboard_layout from u32 to String for proper display
- Add rust-cache to CI and dbus-1-dev dependency

src/main.rs

@@ -724,7 +724,7 @@ fn main() -> Result<(), Box<dyn Error>> {
         }
 
         let mut status = state.system_manager.get_status();
-        status.keyboard_layout = Some(state.current_layout);
+            status.keyboard_layout = Some(state.current_layout.to_string());
 
         if let Ok(mut lm) = state.lock_manager.lock() {
             lm.set_system_status(status);