fix(desktop): correct pipe handling for array column specs and kets

[lightfront]

What this fixes

Two distinct bugs in latexNormalize.ts pipe (|) handling that surface as broken math rendering in the chat. Both are edge cases of the existing | → \vert rule that PR #3666 established.

1. Array column specs corrupted — KaTeX parse error

\begin{array}{c|c} was rewritten to \begin{array}{c\vert c}, causing:

KaTeX parse error: Unknown column alignment: \vert

In LaTeX, the | inside an array/tabular column specification means "draw a vertical rule" between columns. It must not be rewritten to \vert.

Fix: COLUMN_SPEC_ENVS lists environments whose first {...} argument is a column spec (array, tabular, tabularx, longtable, subarray). When \begin{<env>} is encountered, the column-spec brace group is copied verbatim — no | or % rewriting. Pipes outside the spec still convert to \vert normally.

2. Ket delimiters in GFM tables render as double bars

In Markdown tables, | is the column delimiter. To write a ket |ψ⟩ inside a table cell, the | must be escaped as \| — otherwise the table breaks. But \| in LaTeX/KaTeX is the parallel-to symbol (‖, U+2225), the heavy double bar used for norms, not the light single bar (∣, U+2223) that kets use. The result: |uud⟩ rendered as ‖uud⟩.

Fix: fixKetPipes() converts \| → \vert when it is:

• A ket opener: \|...\rangle (unpaired, ends in \rangle)
• A bra closer: \langle...\| (unpaired, starts with \langle)

While preserving norms: matched \|...\| pairs keep the double bar. Disambiguation is by forward scan to the next \| or \rangle, with a backward scan for unmatched \langle to catch bra closers at the end of an expression.

Pattern	Meaning	Result
|uud\rangle	ket	→ \vert (single bar ∣)
\langle\psi|	bra	→ \vert (single bar ∣)
\langle x | y \rangle	inner product	→ \vert (single bar ∣)
|x|	norm	kept as | (double bar ‖)

Testing

• 121 passed, 0 failed (was 109; +12 new golden tests)
• TypeScript compiles cleanly
• New tests cover column-spec preservation, ket/bra conversion, norm preservation, and end-to-end KaTeX render of all three cases through the full normalizeMath → remark-math → rehype-katex pipeline

Relationship to other PRs

Related to #3666 (inline math rendering hardening) — that PR established the math pre-pass infrastructure and the | → \vert rule. This PR fixes two edge cases of that rule. Independent of #3750 (\slashed) and #4216 (Young diagrams).