fix: add frontend nginx.conf, remove obsolete docker-compose version

docker-compose.prod.yml

@@ -1,5 +1,3 @@
-version: "3.9"
-
 services:
   postgres:
     image: postgres:16-alpine

docker-compose.yml

@@ -1,5 +1,3 @@
-version: "3.9"
-
 services:
   postgres:
     image: postgres:16-alpine

frontend/nginx.conf

@@ -0,0 +1,10 @@
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+}