fix: use libgl1 and pin to bookworm (libgl1-mesa-glx removed in trixie)

Dockerfile

@@ -1,10 +1,11 @@
-FROM python:3.11-slim
+FROM python:3.11-slim-bookworm
 
 WORKDIR /app
 
 # Install system dependencies for OpenCV
+# libgl1-mesa-glx was removed in Debian Trixie — use libgl1 instead
 RUN apt-get update && apt-get install -y --no-install-recommends \
-    libgl1-mesa-glx libglib2.0-0 libsm6 libxrender1 libxext6 \
+    libgl1 libglib2.0-0 libsm6 libxrender1 libxext6 \
     && rm -rf /var/lib/apt/lists/*
 
 COPY requirements.txt .