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.

GPU-FIX-README.md

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+# GPU Fix Guide for Nebula Browser
+
+## Common GPU Issues
+
+Nebula Browser is an Electron-based application that uses Chromium's rendering engine. Some systems may experience GPU-related issues such as:
+- Black/blank screens
+- Webviews not loading content
+- Flickering or visual artifacts
+- Application crashes
+
+## SteamOS / Steam Deck
+
+### Symptoms
+On SteamOS (Steam Deck), you may see:
+- Browser chrome loads (tab bar, URL bar visible)
+- Web page content area is completely black/empty
+- No error messages visible
+
+### Cause
+This is caused by GPU compositing conflicts between Electron's Chromium renderer and Gamescope (Steam Deck's compositor). The AMD GPU in Steam Deck handles nested compositor contexts differently.
+
+### Solution
+
+**Option 1: Automatic Detection (Recommended)**
+The latest version of Nebula automatically detects SteamOS/Gamescope and applies the necessary fixes. Simply update to the latest version.
+
+**Option 2: Manual Launch Script**
+Use the provided `start-steamos.sh` script:
+```bash
+chmod +x start-steamos.sh
+./start-steamos.sh
+```
+
+**Option 3: Command-line Flags**
+If running manually, add these flags:
+```bash
+electron . --ozone-platform=x11 --disable-gpu-compositing --disable-gpu-vsync --no-sandbox --disable-dev-shm-usage
+```
+
+**Option 4: Environment Variable**
+Set the `ELECTRON_OZONE_PLATFORM_HINT` environment variable:
+```bash
+export ELECTRON_OZONE_PLATFORM_HINT=x11
+npm start
+```
+
+## Linux (General)
+
+### Wayland
+If running on a Wayland compositor (GNOME Wayland, KDE Wayland, Sway, etc.):
+```bash
+electron . --ozone-platform=wayland --enable-features=UseOzonePlatform,WaylandWindowDecorations
+```
+
+### X11
+For X11 sessions:
+```bash
+electron . --ozone-platform=x11
+```
+
+### NVIDIA GPUs
+If using NVIDIA proprietary drivers:
+```bash
+electron . --disable-gpu-sandbox --no-sandbox
+```
+
+## Windows
+
+### Intel/AMD Integrated Graphics Issues
+If experiencing blank screens on Windows with integrated graphics:
+1. Try running with `start-gpu-safe.bat`
+2. Update your graphics drivers
+3. Disable hardware acceleration in settings (if available)
+
+### Multiple GPU Systems
+On laptops with both integrated and discrete GPUs:
+- Right-click the Nebula shortcut
+- Select "Run with graphics processor"
+- Choose your dedicated GPU
+
+## macOS
+
+macOS typically has fewer GPU issues, but if problems occur:
+```bash
+electron . --disable-gpu
+```
+
+## Diagnostic Information
+
+To see GPU information and diagnostics:
+1. Open Nebula Browser
+2. Navigate to `nebula://gpu` or `chrome://gpu`
+3. Check the "Graphics Feature Status" section
+
+## Reporting Issues
+
+If none of the above solutions work, please report the issue with:
+1. Operating system and version
+2. GPU model and driver version
+3. Contents of `chrome://gpu` page
+4. Any error messages from terminal/console