scoring: preserve backslash-pipe IDs in Markdown tables #113

An ID with a backslash followed by a pipe produces an even backslash run before the pipe in the Markdown cell, allowing GFM to split another column. CSV values and decisions remain correct. Escape existing backslashes as well as pipes and add a rendered-table regression.

Confirmed at a575437 from PR #4 discussion_r4114179699. Deferred under the approved convergence rule: no source-input loss or false PASS was found.