fix(nginx): Add Docker DNS resolver for Swarm/dynamic service discovery (v2.2.3)

Fixes 502 Bad Gateway on root path in Docker Swarm by adding DNS resolver
  configuration (127.0.0.11) and dynamic DNS resolution for all proxy_pass 
  directives. This ensures nginx resolves backend service IPs on each request 
  rather than caching them at startup.

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "picpeak-backend",
-  "version": "2.2.2",
+  "version": "2.2.3",
   "description": "Backend for PicPeak event photo sharing platform",
   "main": "server.js",
   "scripts": {

frontend/nginx.conf

@@ -4,6 +4,10 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
+    # Docker DNS resolver for dynamic service discovery (required for Swarm/Compose)
+    resolver 127.0.0.11 valid=10s ipv6=off;
+    resolver_timeout 5s;
+
     # Allow larger file uploads (up to 100MB)
     client_max_body_size 100M;
     client_body_timeout 300s;
@@ -43,7 +47,9 @@ server {
 
     # API proxy
     location /api {
-        proxy_pass http://backend:3000;
+        # Use variable to force DNS resolution per request (required for Docker Swarm)
+        set $backend_upstream backend;
+        proxy_pass http://$backend_upstream:3000;
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection 'upgrade';
@@ -53,7 +59,7 @@ server {
         proxy_set_header X-Forwarded-Proto $scheme;
         proxy_cache_bypass $http_upgrade;
         proxy_read_timeout 86400;
-        
+
         # Allow larger uploads for API endpoints
         client_max_body_size 100M;
         client_body_timeout 300s;
@@ -61,13 +67,14 @@ server {
 
     # Photo serving proxy
     location /photos {
-        proxy_pass http://backend:3000;
+        set $backend_upstream backend;
+        proxy_pass http://$backend_upstream:3000;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         proxy_set_header X-Forwarded-Proto $scheme;
-        
+
         # Cache photos
         proxy_cache_valid 200 302 1d;
         proxy_cache_valid 404 1m;
@@ -75,13 +82,14 @@ server {
 
     # Thumbnail serving proxy
     location /thumbnails {
-        proxy_pass http://backend:3000;
+        set $backend_upstream backend;
+        proxy_pass http://$backend_upstream:3000;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         proxy_set_header X-Forwarded-Proto $scheme;
-        
+
         # Cache thumbnails
         proxy_cache_valid 200 302 7d;
         proxy_cache_valid 404 1m;
@@ -90,13 +98,14 @@ server {
     # Uploads serving proxy (logos, favicons, watermarks)
     # ^~ modifier stops regex matching, ensuring uploads are proxied not served locally
     location ^~ /uploads {
-        proxy_pass http://backend:3000;
+        set $backend_upstream backend;
+        proxy_pass http://$backend_upstream:3000;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         proxy_set_header X-Forwarded-Proto $scheme;
-        
+
         # Cache uploads
         proxy_cache_valid 200 302 7d;
         proxy_cache_valid 404 1m;
@@ -104,7 +113,9 @@ server {
 
     # Delegate root requests to backend for public landing page handling
     location = / {
-        proxy_pass http://backend:3000/;
+        # Use variable to force DNS resolution per request (required for Docker Swarm)
+        set $backend_upstream backend;
+        proxy_pass http://$backend_upstream:3000/;
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection 'upgrade';

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "picpeak-frontend",
   "private": true,
-  "version": "2.2.2",
+  "version": "2.2.3",
   "type": "module",
   "scripts": {
     "dev": "vite",