bug: Syntax error / parser crash when a node label contains brackets inside double quotes (e.g., "xx[]yy")

Describe the bug

When rendering a Flowchart using beautiful-mermaid, the parser crashes with a syntax/render error if a node text contains brackets [] even when the entire string is properly wrapped in standard double quotes "".

It seems the lexer/parser inappropriately triggers a node closure rule when encountering the ] character inside the string literal, rather than treating the quoted text as a pure string.

To Reproduce

Try to render the following valid Mermaid syntax in the editor:

graph LR
  A["test [] brackets"]
  B["xx[]yy"]
  A --> B

Expected behavior

The diagram should render successfully, displaying two rectangular nodes with the literal texts test [] brackets and xx[]yy.

Actual behavior

The rendering pipeline fails completely / throws a syntax error.

Context

• Library: beautiful-mermaid (via Agents Craft Editor)
• Output type: SVG / Canvas Live View

Additional note

Since htmlLabels is disabled by default in this project (htmlLabels: false), using HTML entities like [ and ] also crashes the parser. This leaves users with absolutely no workaround to display the [] characters inside flowcharts.