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.

backend/migrations/20260131163528_trust_forwarded_proto.js

@@ -0,0 +1,31 @@
+import { migrate as logger } from "../logger.js";
+
+const migrateName = "redirect_auto_scheme";
+
+/**
+ * Migrate
+ *
+ * @see http://knexjs.org/#Schema
+ *
+ * @param   {Object} knex
+ * @returns {Promise}
+ */
+const up = function (knex) {
+    return knex.schema.alterTable('proxy_host', (table) => {
+        table.tinyint('trust_forwarded_proto').notNullable().defaultTo(0);
+    });
+};
+
+/**
+ * Undo Migrate
+ *
+ * @param   {Object} knex
+ * @returns {Promise}
+ */
+const down = function (knex) {
+    return knex.schema.alterTable('proxy_host', (table) => {
+        table.dropColumn('trust_forwarded_proto');
+    });
+};
+
+export { up, down };