Fix Dockerfile package name for newer Debian versions

Changed libgl1-mesa-glx to libgl1 for compatibility with Debian Trixie.
The older package name has been replaced in newer Debian releases.

backend/Dockerfile

@@ -4,7 +4,7 @@ WORKDIR /app
 
 # Install system dependencies
 RUN apt-get update && apt-get install -y \
-    libgl1-mesa-glx \
+    libgl1 \
     libglib2.0-0 \
     && rm -rf /var/lib/apt/lists/*