fix: trust proxy forwarded headers so login works behind Caddy

Behind Jambotron's Caddy the app saw http while the browser used https,
so same-domain requests looked cross-origin and @CrossOrigin answered
403 on /api/auth/signin. server.forward-headers-strategy=framework makes
the app use X-Forwarded-Proto/Host; app.origin can be set via APP_ORIGIN.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

spring-angular-ui/nginx.conf

@@ -1,3 +1,9 @@
+# Схема исходного запроса: за Caddy (https) — из его X-Forwarded-Proto, иначе своя
+map $http_x_forwarded_proto $forwarded_proto {
+    default $http_x_forwarded_proto;
+    ""      $scheme;
+}
+
 server {
     listen 80;
     server_name _;
@@ -12,7 +18,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $forwarded_proto;
     }
 
     # Маршруты Angular (/admin, /tutorials/1 ...) отдаём через index.html