Add SteamOS GPU fixes and launch script

Introduces SteamOS/Steam Deck detection and GPU configuration in gpu-config.js, adds a dedicated start-steamos.sh launch script, and updates package.json with new scripts for SteamOS and Linux GPU-safe launches. Also adds a comprehensive GPU troubleshooting guide in GPU-FIX-README.md to address rendering issues on various platforms.

package.json

@@ -5,6 +5,8 @@
   "main": "main.js",
   "scripts": {
     "start": "electron .",
+    "start:steamos": "electron . --ozone-platform=x11 --disable-gpu-compositing --disable-gpu-vsync --no-sandbox --disable-dev-shm-usage --disable-features=VizDisplayCompositor",
+    "start:linux-safe": "electron . --disable-gpu --disable-gpu-compositing --no-sandbox",
     "dist": "electron-builder",
     "run": "electron ."
   },