feat(dashboard): add sensitive data toggle to flow chart

Add an eye toggle in the flow section header that masks sensitive node
labels (users, tokens, nodes, groups, channels) in the Sankey while keeping
model names visible. Masking only rewrites display text; nodes stay distinct
via their key so graph structure, links, and highlighting are unaffected.

web/default/src/i18n/locales/zh.json

@@ -2051,6 +2051,7 @@
     "Hidden — verify to reveal": "隐藏 — 验证以显示",
     "Hide": "隐藏",
     "Hide API key": "隐藏 API 密钥",
+    "Hide sensitive data": "隐藏敏感数据",
     "Hide setup guide": "隐藏设置引导",
     "High Performance": "高性能",
     "High-risk operation confirmation": "高危操作确认",
@@ -3870,6 +3871,7 @@
     "Shorten": "缩词",
     "Show": "显示",
     "Show All": "显示全部",
+    "Show sensitive data": "显示敏感数据",
     "Show all providers including unbound": "显示所有提供商（包括未绑定）",
     "Show only bound providers": "仅显示已绑定的提供商",
     "Show or hide flow columns": "显示或隐藏分流列",