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>

system1-factory/web/nginx.conf

@@ -1,6 +1,7 @@
 server {
     listen 80;
     server_name _;
+    resolver 127.0.0.11 valid=10s ipv6=off;
 
     client_max_body_size 50M;
 
@@ -25,7 +26,8 @@ server {
 
     # API 프록시 (System 1 API)
     location /api/ {
-        proxy_pass http://system1-api:3005/api/;
+        set $upstream http://system1-api:3005;
+        proxy_pass $upstream$request_uri;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
@@ -35,14 +37,17 @@ server {
 
     # 업로드 파일 프록시 (^~ 로 regex location보다 우선 매칭)
     location ^~ /uploads/ {
-        proxy_pass http://system1-api:3005/uploads/;
+        set $upstream http://system1-api:3005;
+        proxy_pass $upstream$request_uri;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
     }
 
     # FastAPI Bridge 프록시
     location /fastapi/ {
-        proxy_pass http://system1-fastapi:8000/;
+        set $upstream http://system1-fastapi:8000;
+        rewrite ^/fastapi/(.*)$ /$1 break;
+        proxy_pass $upstream;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
@@ -52,7 +57,9 @@ server {
 
     # SSO Auth 프록시 (gateway에서 이관)
     location /auth/ {
-        proxy_pass http://sso-auth:3000/api/auth/;
+        set $upstream http://sso-auth:3000;
+        rewrite ^/auth/(.*)$ /api/auth/$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;
@@ -61,7 +68,6 @@ server {
 
     # AI Service 프록시 (gateway에서 이관)
     location /ai-api/ {
-        resolver 8.8.8.8 valid=300s ipv6=off;
         set $ai_upstream https://ai.hyungi.net;
         rewrite ^/ai-api/(.*) /api/ai/$1 break;
         proxy_pass $ai_upstream;