fix(infra): nginx 동적 DNS resolve + Docker 헬스체크 추가

컨테이너 재생성 시 502 Bad Gateway 방지:
- 모든 nginx proxy_pass를 set $upstream 변수 방식으로 전환 (9개 파일, 24개 location)
- resolver 127.0.0.11 valid=10s ipv6=off 통합 선언
- ai-api location의 개별 resolver 8.8.8.8 제거 (server-level로 통합)
- 10개 API 서비스에 healthcheck 추가 (Node: wget, Python: urllib)
- 모든 web/gateway depends_on을 condition: service_healthy로 강화

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tkeg/web/nginx.conf

@@ -1,13 +1,16 @@
 server {
     listen 80;
     server_name localhost;
+    resolver 127.0.0.11 valid=10s ipv6=off;
     root /usr/share/nginx/html;
     index index.html;
 
     client_max_body_size 100M;
 
     location /api/ {
-        proxy_pass http://tkeg-api:8000/;
+        set $upstream http://tkeg-api:8000;
+        rewrite ^/api/(.*)$ /$1 break;
+        proxy_pass $upstream;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;