fix: Add Nginx configuration update to CI/CD deployment

CRITICAL FIX for 502 Bad Gateway error:
- Green-Blue deployment was switching to new port (5004)
- But Nginx config was still pointing to old port (5003)
- Result: direct port access worked, but Nginx proxy returned 502

CHANGES:
1. deploy_gb.sh: Remove sudo calls (requires root credentials)
   - Script cannot use sudo without NOPASSWD configuration
   - Nginx update now handled by CI post-deploy script

2. .gitea/workflows/deploy.yml: Add Nginx update step after Green-Blue deployment
   - Read new active port from taxbaik_port file
   - Update /etc/nginx/sites-available/default proxy_pass
   - Validate Nginx syntax
   - Reload Nginx with new configuration
   - Runs as root (CI runner privilege) - no sudo needed

RESULT:
- Nginx always points to current active port
- 502 errors prevented
- Seamless zero-downtime Green-Blue deployment

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -193,6 +193,13 @@ jobs:
           chmod +x "\$DEPLOY_DIR/deploy_gb.sh"
           "\$DEPLOY_DIR/deploy_gb.sh" "\$DEPLOY_DIR"
 
+          echo "--- [4.5/5] Nginx 설정 업데이트 ---"
+          TARGET_PORT=\$(cat \$DEPLOY_HOME/taxbaik_port | tr -d '[:space:]')
+          sed -i "s|proxy_pass.*http://127.0.0.1:500[34];|proxy_pass         http://127.0.0.1:\${TARGET_PORT};|g" /etc/nginx/sites-available/default
+          nginx -t || { echo "❌ Nginx syntax error" >&2; exit 1; }
+          systemctl reload nginx
+          echo "✓ Nginx reloaded with port \${TARGET_PORT}"
+
           echo "--- [5/5] 헬스 체크 (최대 60초) ---"
           ATTEMPTS=20
           for i in \$(seq 1 \$ATTEMPTS); do

deploy_gb.sh

@@ -103,10 +103,11 @@ if [ "$SUCCESS" = "false" ]; then
   exit 1
 fi
 
-# 6. Switch Traffic
+# 6. Switch Traffic (Nginx update handled by CI post-deploy script)
 echo "=== Switching Traffic to Port $TARGET_PORT ==="
 echo "$TARGET_PORT" > "$PORT_FILE"
 echo "✓ Traffic routed to $TARGET_PORT"
+echo "⚠️  Note: Nginx will be updated by CI post-deploy script (requires root)"
 
 # 7. Terminate Old App
 echo "=== Stopping Old App on Port $ACTIVE_PORT ==="