fix: add automatic nginx upstream fix for staging 502 errors

- Add post-deployment fix in build-image.yml workflow to automatically fix nginx upstream configuration
- nginx sites-available/default uses 127.0.0.1:9000 but PHP-FPM runs in staging-app container
- Fix runs automatically after each staging deployment
- Add troubleshooting documentation for staging 502 errors
- Add Ansible playbooks for quick fix and diagnosis

.gitea/workflows/build-image.yml

@@ -990,6 +990,15 @@ jobs:
             echo "🔄 Restarting staging-app to ensure all services are up-to-date..."
             docker compose restart staging-app || echo "⚠️  Failed to restart staging-app"
             
+            # Fix nginx upstream configuration - critical fix for 502 errors
+            # sites-available/default uses 127.0.0.1:9000 but PHP-FPM runs in staging-app container
+            echo "🔧 Fixing nginx PHP-FPM upstream configuration (post-deploy fix)..."
+            sleep 5
+            docker compose exec -T staging-nginx sed -i '/upstream php-upstream {/,/}/s|server 127.0.0.1:9000;|server staging-app:9000;|g' /etc/nginx/sites-available/default || echo "⚠️  Upstream fix (127.0.0.1) failed"
+            docker compose exec -T staging-nginx sed -i '/upstream php-upstream {/,/}/s|server localhost:9000;|server staging-app:9000;|g' /etc/nginx/sites-available/default || echo "⚠️  Upstream fix (localhost) failed"
+            docker compose exec -T staging-nginx nginx -t && docker compose restart staging-nginx || echo "⚠️  Nginx config test or restart failed"
+            echo "✅ Nginx configuration fixed and reloaded"
+            
             echo "⏳ Waiting for services to stabilize..."
             sleep 10
             echo "📊 Container status:"