fix: escape pipe characters in column titles

[greymoth-jp]

Cell values are escaped through toCellText so a | becomes \|, and there is a test for it ("escapes pipe characters in cells by default"). Column titles skip that step: getColumnTitle returns the supplied name, the toHeaderTitle result, or the cased key verbatim. So a pipe in a column title lands in the header row unescaped:

import { tablemark } from "tablemark";

tablemark([{ range: 5 }, { range: 12 }], { columns: [{ name: "Min | Max" }] });

| Min | Max |
| :-------- |
| 5         |
| 12        |

The header row now has two cells while the delimiter row has one. The GFM tables spec requires the header row to match the delimiter row in cell count, otherwise the block is not parsed as a table. Rendered through marked the whole table collapses into a paragraph. The same "Min | Max" placed in a body cell comes out as Min \| Max, so the two paths disagree.

Fix

Escape pipes in the resolved column title the same way cell values are escaped. I pulled the existing pipe escaping out of toCellText into a small escapePipes helper so both the cell path and the title path use one routine. With the fix the example becomes:

| Min \| Max |
| :--------- |
| 5          |
| 12         |

which parses as a one column table with the header Min | Max.

Tests

Added "escapes pipe characters in column titles by default" alongside the existing cell test. Reverting the change makes the new snapshot mismatch. Full suite passes (76), and oxlint, eslint, prettier and tsc --noEmit are clean.

[haltcase-bot]

Hey @greymoth-jp, thanks for contributing! If you haven't read the contributing guide that outlines the process, you can do so here.

Maintainers: once checks have passed, comment !release this and I'll begin merging this for you.

[greymoth-jp]

Closing this to clean up my open PRs. It's a small change and not really worth taking up your review time. Sorry for the noise.