feat: update nginx configuration to use forwarded_proto variable and add .env.example for local setup

.env.example

@@ -0,0 +1,10 @@
+# Copy to .env for local use. Configure production values in your deployment platform's secret manager.
+MONGO_ROOT_USERNAME=lmnp
+MONGO_ROOT_PASSWORD=change-me-to-a-long-random-url-safe-password
+OIDC_ISSUER_URI=https://identity.example.com/realms/lmnp
+OIDC_CLIENT_ID=lmnp-client
+OIDC_CLIENT_SECRET=replace-with-your-oidc-client-secret
+
+# Development-only host ports used by compose.dev.yml.
+BACKEND_PORT=8080
+FRONTEND_PORT=8081