Fix nginx log path to stdout/stderr and set MPLCONFIGDIR=/tmp with proper tmp permissions

Dockerfile

@@ -37,7 +37,7 @@ COPY backend/ ./backend/
 FROM python:3.11-slim AS runtime
 ENV PYTHONUNBUFFERED=1 PIP_NO_CACHE_DIR=1 PORT=7860 \
     PATH="/opt/venv/bin:${PATH}" \
-    MPLCONFIGDIR=/tmp/matplotlib
+    MPLCONFIGDIR=/tmp 
 
 WORKDIR /app
 
@@ -47,6 +47,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libgomp1 libopenblas0 \
  && rm -rf /var/lib/apt/lists/*
 
+RUN install -d -m 0777 /tmp/nginx/client_body /tmp/nginx/proxy /tmp/nginx/fastcgi /tmp/nginx/uwsgi /tmp/nginx/scgi
+
 # 建立可寫暫存
 RUN mkdir -p /tmp/nginx/client_body /tmp/nginx/proxy /tmp/nginx/fastcgi /tmp/nginx/uwsgi /tmp/nginx/scgi \
     /tmp/matplotlib
@@ -61,6 +63,9 @@ COPY --from=be /app/backend /app/backend
 # nginx 主設定
 COPY nginx.conf.template /etc/nginx/nginx.conf
 
+RUN printf "access_log /dev/stdout;\nerror_log /dev/stderr info;\n" \
+  > /etc/nginx/conf.d/log_to_stdout.conf
+
 # 放一個 http 級別的 drop-in，避免高風險 sed
 RUN printf "client_max_body_size 100M;\nclient_body_temp_path /tmp/nginx/client_body;\nproxy_temp_path /tmp/nginx/proxy;\nfastcgi_temp_path /tmp/nginx/fastcgi;\nuwsgi_temp_path /tmp/nginx/uwsgi;\nscgi_temp_path /tmp/nginx/scgi;\n" \
     > /etc/nginx/conf.d/temp_paths.conf