fix(web): improve error handling and API health check logic

- Refactored the API health check to handle errors more gracefully, providing clearer feedback on loading issues.
- Updated the NGINX configuration to use a dynamic upstream variable for better resilience against IP changes in Docker.
- Enhanced user notifications for API availability and data loading errors, including instructions for local demo setup.

deploy/docker/evobgp-web/nginx.conf

@@ -5,8 +5,13 @@ server {
     gzip on;
     gzip_types text/css application/javascript application/json image/svg+xml;
 
+    # Docker embedded DNS: без resolver nginx кэширует IP upstream при старте —
+    # после recreate evobgp-all остаётся 502 (connection refused на старый IP).
+    resolver 127.0.0.11 valid=10s ipv6=off;
+    set $evobgp_upstream evobgp-api;
+
     location /v1/ {
-        proxy_pass http://evobgp-api:8080/v1/;
+        proxy_pass http://$evobgp_upstream:8080/v1/;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
@@ -15,7 +20,7 @@ server {
     }
 
     location = /metrics {
-        proxy_pass http://evobgp-api:8080/metrics;
+        proxy_pass http://$evobgp_upstream:8080/metrics;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
     }