Structured CSV and TSV diffs

Changed .csv and .tsv files can switch between the ordinary Code diff and an accessible Table diff. RFC-4180 quoting, escaped delimiters, CRLF/LF, and multiline quoted fields are supported. Exact rows align first; adjacent removals/additions are paired into changed records with semantic row and cell status.

Code remains the source-of-truth view for line selection and discard. Table never generates or applies a patch. Parsing stops at 512 KiB per side, 500 records, 128 columns, 20,000 cells, or 64 KiB per cell; malformed/oversized input deterministically falls back to Code.

Visible and assistive copy follows English, playful Hong Kong Cantonese, or bilingual mode. Tests cover quoting, multiline data, row/cell alignment, accessibility, bounds, fallback, and the interactive view switch. See Structured data and TGA previews for the full parser contract.