feat: add Docker publishing via GitHub Actions

Former-commit-id: 36c92881c8

backend/Dockerfile

@@ -9,6 +9,13 @@ RUN pip install --no-cache-dir -r requirements.txt
 # Copy source code
 COPY . .
 
+# Create a non-root user for security
+RUN adduser --system --uid 1001 backenduser \
+    && chown -R backenduser /app
+
+# Switch to the non-root user
+USER backenduser
+
 # Expose port
 EXPOSE 8000