fix: correct file ownership for non-root user in Docker

Add --chown=appuser:appuser to COPY commands in runtime stage to ensure
the appuser can read the copied files. Without this, Python fails with
PermissionError when importing modules.

Dockerfile

@@ -28,10 +28,10 @@ RUN useradd --create-home --shell /bin/bash appuser
 WORKDIR /app
 
 # Copy virtual environment from builder
-COPY --from=builder /app/.venv /app/.venv
+COPY --from=builder --chown=appuser:appuser /app/.venv /app/.venv
 
 # Copy source code
-COPY --from=builder /app/src ./src
+COPY --from=builder --chown=appuser:appuser /app/src ./src
 
 # Set environment
 ENV PATH="/app/.venv/bin:$PATH"