Equation

Simple LaTeX subset — see src/core/equation/index.ts.

• MAX_LATEX_LENGTH = 2000, blocked \\input, \\def, balanced braces
• validateLatex(latex) → {valid,errors}
• latexToHtml(latex) → <span class="pde-frac"> etc., handles \\frac, \\sqrt, ^/_, greek
• latexToPlainText for PDF fallback $latex$
• equationCss for pde-equation, pde-frac, pde-sqrt

Nodes: InlineEquationNode (type:"equation", latex, display?) and EquationBlockNode (type:"equation-block"), factories createEquation/createEquationBlock, validated in validator.ts, rendered in editor-web/view and export/*.