fix(nodes): make node API tokens write-only (#5613)

* fix(nodes): make node API tokens write-only

* fix(nodes): keep token optional on edit for write-only API tokens

NodeView no longer returns apiToken, so the edit form must consume hasApiToken and not require re-entering the token. Relaxes the form validation on edit, adds a keep-current placeholder, and adds the i18n key to all 13 locales.

internal/web/translation/zh-CN.json

@@ -1007,6 +1007,7 @@
       "apiToken": "API 令牌",
       "apiTokenPlaceholder": "远程面板设置页中的令牌",
       "apiTokenHint": "远程面板在 安全设定 → API 令牌 中显示其 API 令牌。",
+      "apiTokenKeepHint": "留空以保留当前令牌",
       "regenerate": "重新生成令牌",
       "regenerateConfirm": "重新生成会使当前令牌失效。任何使用该令牌的中央面板都会失去访问权限，直至更新。是否继续？",
       "allowPrivateAddress": "允许私有地址",