feat(nginx): bake default white-label routing config, closes #1 (#2)

## Summary

- Add `nginx.conf.template` with full routing: admin/CMS surfaces → `cms:5555`, uploads → `cms:5555` (cached), `/api` → `shop:9999` (no cache), `/` → `shop:9999` (cached)
- Update `docker-entrypoint.sh` to render template via `envsubst` at startup; skip if adapter has already mounted its own config
- Update `Dockerfile` to `COPY nginx.conf.template` into image
- Bump CHANGELOG to v0.1.1

## Test plan

- [ ] Build image locally: `docker build -t libreshop/nginx:test libreshop/nginx/`
- [ ] Smoke test white-label default: no env overrides → confirm rendered `/etc/nginx/nginx.conf` contains `cms:5555` and `shop:9999`
- [ ] Smoke test env override: `NGINX_UPSTREAM_SHOP=shop:8080` → confirm substitution
- [ ] Smoke test adapter override: mount custom `nginx.conf` via compose `configs:` → confirm "adapter-provided nginx.conf detected" log line
- [ ] Deploy libreshop/demo with `nginx:v0.1.1` → confirm `/admin` returns 200

Closes #1

Co-authored-by: Michael Czechowski <michael.c@re-cinq.com>
Reviewed-on: #2

docker-entrypoint.sh

@@ -1,19 +1,36 @@
 #!/usr/bin/env bash
 set -e
 
-echo "Generated nginx.conf:"
-echo ""
+# Defaults — overridable via env in compose / docker run.
+: "${NGINX_UPSTREAM_SHOP:=shop:9999}"
+: "${NGINX_UPSTREAM_CMS:=cms:5555}"
+: "${NGINX_CACHE_LIFETIME:=1h}"
+export NGINX_UPSTREAM_SHOP NGINX_UPSTREAM_CMS NGINX_CACHE_LIFETIME
+
+# Render the template only when the nginx.conf in place is the
+# upstream nginx-image stock default. Adapters that mount their own
+# config via compose `configs:` (e.g. mp) get the file replaced
+# before this script runs; we detect that by the absence of the
+# stock `worker_processes  auto;` line and leave that file alone.
+if [ -f /etc/nginx/nginx.conf.template ] \
+   && grep -q "worker_processes  auto;" /etc/nginx/nginx.conf 2>/dev/null; then
+  envsubst '${NGINX_UPSTREAM_SHOP} ${NGINX_UPSTREAM_CMS} ${NGINX_CACHE_LIFETIME}' \
+    < /etc/nginx/nginx.conf.template \
+    > /etc/nginx/nginx.conf
+  echo "→ libreshop default nginx.conf rendered from template"
+else
+  echo "→ adapter-provided nginx.conf detected; leaving untouched"
+fi
+
+mkdir -p /cache/shop /cache/uploads /cache/api
+
+echo "Effective nginx.conf:"
+echo "---"
 cat /etc/nginx/nginx.conf
+echo "---"
 
-mkdir -p /cache/shop
-mkdir -p /cache/uploads
-mkdir -p /cache/api
-
-echo "Starting nginx"
-echo "NGINX_DEBUG=${NGINX_DEBUG}"
-# Start Nginx
 if [ "$NGINX_DEBUG" = "true" ]; then
-  sed -i 's/error\.log warn/error.log debug/' /etc/nginx/nginx.conf
+  perl -i -pe 's|error_log /dev/stdout error|error_log /dev/stdout debug|' /etc/nginx/nginx.conf
   exec nginx-debug -g 'daemon off;'
 else
   exec nginx -g 'daemon off;'