fix: clean up nginx read-only filesystem approach (#125)

Remove Dockerfile /tmp workaround hacks (NGINX_ENVSUBST_OUTPUT_DIR and sed).
Use tmpfs with uid=101,gid=101 in docker-compose.yml instead, so the
nginx user can write to /etc/nginx/conf.d directly under read_only: true.

docker-compose.yml

@@ -52,7 +52,7 @@ services:
       - /tmp:noexec,nosuid,size=64m
       - /var/cache/nginx:noexec,nosuid,size=64m
       - /var/run:noexec,nosuid,size=64m
-      - /etc/nginx/conf.d:noexec,nosuid,size=1m
+      - /etc/nginx/conf.d:noexec,nosuid,size=1m,uid=101,gid=101
     cap_drop:
       - ALL
 

frontend/Dockerfile

@@ -32,11 +32,6 @@ RUN npm run build
 # -----------------------------------------------------------------------------
 FROM nginxinc/nginx-unprivileged:1.27-alpine AS runner
 
-# Redirect envsubst output to /tmp (writable under read_only: true)
-# and update nginx main config to include from there instead of /etc/nginx/conf.d/
-ENV NGINX_ENVSUBST_OUTPUT_DIR=/tmp
-RUN sed -i 's|include /etc/nginx/conf.d/\*.conf;|include /tmp/default.conf;|' /etc/nginx/nginx.conf
-
 # Copy custom nginx config as template for envsubst processing
 # nginx-unprivileged automatically substitutes env vars in .template files
 COPY nginx.conf /etc/nginx/templates/default.conf.template