feat: respect LOG_LEVEL in frontend nginx container (#212)

Add entrypoint wrapper that translates LOG_LEVEL into nginx
access_log control. When LOG_LEVEL is warn or higher, nginx
access logs are suppressed. The frontend container now receives
LOG_LEVEL via env_file (.env) — no new env vars needed.

.env.example

@@ -12,6 +12,9 @@ PGID=1000
 PORT=3000
 CORS_ORIGINS=http://localhost:4174
 LOG_LEVEL=info
+# Levels: debug, info, warn, error, silent
+# Controls: backend Fastify logging, frontend nginx access logs (Docker),
+#           and frontend browser console (via build-time injection)
 
 # Rate limit: max requests per minute per IP (default: 100)
 # Increase for development/testing environments