feat: switch gamepad reader to Linux evdev BTN_* codes

The Joystick API (/dev/input/js*) numbers buttons depending on driver
and connection type. Xbox One controllers via Bluetooth with a Share
button shifted X from button number 2 to 3, silently breaking the
mapping.

The evdev interface provides standardized BTN_* codes (BTN_SOUTH=A,
BTN_NORTH=X, etc.) that remain consistent across Xbox, PlayStation,
and Nintendo controllers over both USB and Bluetooth.

js* devices remain the discovery path, while /sys/class/input/jsN is
used to resolve the corresponding event* device. If the /sys lookup
fails, JoystickFallbackReader falls back to the old Joystick API.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "twitch4steamdeck",
-  "version": "0.4.2",
+  "version": "0.4.3",
   "description": "Twitch-Client für das Steam Deck (Live & VOD, Big-Screen-UI)",
   "main": "out/main/index.js",
   "author": "twitch4steamdeck",