feat(docker): support XUI_PORT runtime override (#5240)

* feat(docker): support XUI_PORT runtime override

Allow deployments to select the panel listener port without mutating the persisted webPort setting. Invalid values fall back to the database-backed port and are covered by parser boundary tests.

* docs: describe XUI_PORT deployment usage

Add commented local and Compose examples, explain runtime precedence, and call out matching Docker bridge port mappings.

docker-compose.yml

@@ -19,6 +19,7 @@ services:
       XRAY_VMESS_AEAD_FORCED: "false"
       XUI_ENABLE_FAIL2BAN: "true"
       # XUI_INIT_WEB_BASE_PATH: "/"
+      # XUI_PORT: "8080"
       # To use PostgreSQL instead of the default SQLite, run:
       #   docker compose --profile postgres up -d
       # and uncomment the two lines below.
@@ -26,6 +27,7 @@ services:
       # XUI_DB_DSN: "postgres://xui:xui@postgres:5432/xui?sslmode=disable"
     tty: true
     ports:
+      # When XUI_PORT is set, publish the same container port (for example "8080:8080").
       - "2053:2053"
     restart: unless-stopped
 
@@ -39,4 +41,4 @@ services:
       POSTGRES_DB: xui
     volumes:
       - $PWD/pgdata/:/var/lib/postgresql/data
-    restart: unless-stopped
+    restart: unless-stopped