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/system.rs

@@ -17,7 +17,7 @@ pub struct SystemStatus {
     pub wifi_strength: Option<u8>,
     pub bluetooth_connected: bool,
     pub bluetooth_devices: Vec<String>,
-    pub keyboard_layout: Option<u32>,
+    pub keyboard_layout: Option<String>,
 }
 
 #[derive(Debug, Clone, Copy)]