Render LaTeX math inside live preview tables

[jsgrrchg]

Markdown live preview now renders inline $…$ and display $$…$$ formulas inside table cells, closing the scope gap left by #496. Frontmatter and the rest of the note keep their current behavior.

How it works

Tables are rendered by a block widget that replaces their source, so the document-level math ranges still exclude Table nodes. Instead:

• Shared scanner (b3160097): the delimiter loop in parseMathRanges is extracted into findMathRanges(text, excluded). Table cells use exactly the same rules as the rest of the note: escaped \$, $$$ runs, prices such as $20 and $30, and no whitespace after the opener. Document behavior is unchanged.
• Cell rendering (6d02c9eb): each text segment of a cell is scanned with code spans excluded. Wikilinks and URLs are already split out and keep their dollars literal. Formulas render through the existing renderMath, so KaTeX options and error handling are shared. The widget only re-renders when the table source changes.

Behavior in cells

• Pipes: as in GFM, an unescaped | always ends a cell, even inside a formula. \| reads as a literal | inside a formula; use \lvert/\rvert or \vert for bars and \Vert for a double bar.
• Formatting: bold and highlights may wrap whole formulas (**$x$ text**, ==$x$==). Formatting that cuts through a formula or sits inside one stays literal, matching the rest of the editor.
• Display math: $$x$$ in a cell uses display-style notation within the line.
• Errors: invalid formulas stay readable, with the KaTeX message on hover.
• Editing: the table widget ignores editor events, so clicking a formula does not reveal it alone. Moving the caret into the table shows its Markdown source, as before. The "Click to edit formula" tooltip is omitted inside tables.

Validation

• 604 editor unit tests passed, including new scanner tests and table integration tests: delimiter rules, code spans, wikilinks, URLs, bold/highlight wrapping and cutting, escaped pipes, invalid formulas, and the raw source while the caret is inside the table.
• All 12 math browser tests passed in Chromium with real KaTeX fonts. A new light/dark test checks that table formulas stay inside their cells, keep the text baseline, show no stray scrollbars, scroll horizontally when wide, and show errors.
• tsc (app and vitest configs) and ESLint on changed files passed.
• Visually checked in light and dark themes; no CSS changes were needed.
• Documented table syntax in docs/markdown-math.md (f94e9ae6).

Out of scope

• The alternative \(…\) / \[…\] delimiters.
• Separately, aliased wikilinks inside tables ([[Note\|alias]]) appear to keep the backslash in their target. This PR does not change that.