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/ja.json

@@ -2051,6 +2051,7 @@
     "Hidden — verify to reveal": "非表示 — 確認して表示",
     "Hide": "非表示にする",
     "Hide API key": "APIキーを非表示",
+    "Hide sensitive data": "機密データを非表示",
     "Hide setup guide": "セットアップガイドを非表示",
     "High Performance": "高パフォーマンス",
     "High-risk operation confirmation": "高リスク操作の確認",
@@ -3870,6 +3871,7 @@
     "Shorten": "短縮",
     "Show": "表示",
     "Show All": "すべて表示",
+    "Show sensitive data": "機密データを表示",
     "Show all providers including unbound": "未バインドを含むすべてのプロバイダーを表示",
     "Show only bound providers": "バインド済みのプロバイダーのみ表示",
     "Show or hide flow columns": "フロー列の表示・非表示",