Return Portal Improvements

Fixed the secret portal completion flow so players can reliably use the free return portal after clearing a secret portal encounter.
Added clearer return behavior for portal exits:
Players can click the return portal when it appears.
Players can type return.
Chinese players can type 返回.
Confirmed that the Chinese recall command remains 回城, while 返回 is used specifically for the free return portal.
Improved guidance so players better understand how to leave a completed portal area and return safely.

Chinese Localization: Level-Up Class Selection

Added Simplified Chinese localization to the level-up class selection panel.
Localized the class advancement modal title, description, class level labels, max-level warnings, and HP/Mana growth text.
Class names and class descriptions now display in Simplified Chinese when the UI language is set to Chinese.
Improved the level-up flow for Chinese-language players so the key class advancement screen is no longer English-only.