fix: protect special characters in math from markdown table parsers (#1462)

[hugogu]

Change Summary

Wiki.js uses markdown-it-attrs which interprets curly braces inside inline math ($...$) as attribute directives, stripping them from the formula. Additionally, markdown table parsers split cells at both | and & characters, breaking formulas containing those symbols.

This fix replaces {, }, |, and & inside math expressions with Unicode Private Use Area placeholders during markdown parsing, then restores them before passing to KaTeX/MathJax for rendering.

• <E000> / <E001>: temporary replacements for { / }
• <E002>: temporary replacement for | (table cell delimiter)
• <E003>: temporary replacement for & (table cell delimiter in multiline tables, used by LaTeX cases/arrays)

The placeholder approach was chosen over HTML escaping because it preserves LaTeX environments like \begin{array} that were broken by the previous {{}} escaping method.

Fixes #1581
Fixes #1462

Test

# Issue #1462 Test Cases

# Latex测试

## 特殊函数

| 符号 | 含义 | 定义/示例 |
|------|------|----------|
| $\zeta(s)$ | 黎曼ζ函数 | $\zeta(2) = \frac{\pi^2}{6}$ |
| $\Gamma(x)$ | 伽马函数 | $\Gamma(n) = (n-1)!$ |
| $\Gamma(z)$ | 伽马函数（复数） | $\Gamma(z) = \int_0^{\infty} t^{z-1}e^{-t}dt$ |
| $B(x, y)$ | 贝塔函数 | $B(x,y) = \frac{\Gamma(x)\Gamma(y)}{\Gamma(x+y)}$ |
| $\psi(x)$ | 双伽马函数 | $\psi(x) = \frac{\Gamma'(x)}{\Gamma(x)}$ |
| $\mathrm{Heaviside}(x)$ | 海维赛德阶跃 | $H(x) = \begin{cases} 1 & x \geq 0 \\ 0 & x < 0 \end{cases}$ |
| $\delta(x)$ | 狄拉克δ函数 | $\int_{-\infty}^{\infty} \delta(x)dx = 1$ |
| $\mathrm{sinc}(x)$ | sinc函数 | $\mathrm{sinc}(x) = \frac{\sin x}{x}$ |
| $\mathrm{rect}(x)$ | 矩形函数 | $\mathrm{rect}(x) = \begin{cases} 1 & |x| \leq 1/2 \\ 0 & \text{其他} \end{cases}$ |
| $\sigma_x, \sigma_y, \sigma_z$ | 泡利矩阵 | $\sigma_x = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}$ |
| $\mathfrak{c}$ | 连续统基数 | $|\mathbb{R}| = \mathfrak{c}$ |
| $\sum_{n \in S}$ | 对集合求和 | $\sum_{n \in \mathbb{N}} \frac{1}{n^2}$ |

## Array Environment

$\begin{array}{lrc} 1 & 2 & 3 \\ 4 & 5 & 6 \end{array}$

text $\begin{array}{lrc} 1 & 2 & 3 \\ 4 & 5 & 6 \end{array}$ text

## Simple Fractions

$\frac{1}{3}$

text $\frac{1}{3}$ text

## Fractions with Superscripts

$\frac{1^{2}}{3^{4}}$

$\frac{1}{3^{4}}$

$\frac{1^{2}}{3}$

## Einstein Field Equation

$G_{\mu\nu} + \Lambda g_{\mu\nu} = \frac{8\pi G}{c^4} T_{\mu\nu}$

## Block Array

$$
\begin{array}{lrc}
1 & 2 & 3 \\
4 & 5 & 6
\end{array}
$$

The latest build by now (2.5.314) render it as

and

After the fix all latex text will be rendered correctly:

and