fix: show sandbox flowcharts on Win7 Chrome and repair common Mermaid syntax

Disable HTML labels so nodes use native SVG text, and rewrite bare edge labels plus invalid class statements before render.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-web/scripts/check-chrome109-css.mjs

@@ -31,6 +31,11 @@ const requiredLegacyFallbacks = [
     pattern: /<InputGroup className="h-auto min-h-16">/,
     description: "Prompt textarea must not rely on :has() for its parent height",
   },
+  {
+    file: "src/core/utils/mermaid.ts",
+    pattern: /htmlLabels:\s*false[\s\S]*secure:\s*\[[\s\S]*"htmlLabels"/,
+    description: "Sandbox flowcharts must use native SVG labels in legacy browsers",
+  },
 ];
 
 for (const file of cssFiles) {