Enhance Dockerfile to create app user and set proper file ownership

Dockerfile

@@ -1,8 +1,14 @@
 FROM python:3.9-slim
 
+# Create app user and directory
+RUN useradd -m appuser && mkdir -p /app && chown appuser:appuser /app
+
 WORKDIR /app
 
-COPY . .
+# Copy files with proper ownership
+COPY --chown=appuser:appuser . .
+
+USER appuser
 
 RUN pip install --no-cache-dir -r requirements.txt