feat: add trust_forwarded_proto option for SSL redirect handling in reverse proxy scenarios

When Nginx is behind another proxy server (like CloudFlare or AWS ALB), the force-SSL
feature can cause redirect loops because Nginx sees the connection as plain HTTP
while SSL is already handled upstream. This adds a new boolean option to trust
the X-Forwarded-Proto header from upstream proxies.

Changes:
- Add `trust_forwarded_proto` column to proxy_host table (migration)
- Update model and API schema to support the new boolean field
- Modify force-ssl Nginx template to check X-Forwarded-Proto/X-Forwarded-Scheme
- Add map directives in nginx.conf to validate and sanitize forwarded headers
- Add advanced option toggle in frontend UI with i18n support (EN/ZH)
- Set proxy headers from validated map variables instead of $scheme

This allows administrators to control SSL redirect behavior when Nginx is deployed
behind a TLS-terminating proxy.

docker/rootfs/etc/nginx/conf.d/include/proxy.conf

@@ -1,7 +1,7 @@
 add_header       X-Served-By $host;
 proxy_set_header Host $host;
-proxy_set_header X-Forwarded-Scheme $scheme;
-proxy_set_header X-Forwarded-Proto  $scheme;
+proxy_set_header X-Forwarded-Scheme $x_forwarded_scheme;
+proxy_set_header X-Forwarded-Proto  $x_forwarded_proto;
 proxy_set_header X-Forwarded-For    $proxy_add_x_forwarded_for;
 proxy_set_header X-Real-IP          $remote_addr;
 proxy_pass       $forward_scheme://$server:$port$request_uri;