ADR-0043 residual: a compound-FK violation's friendly error named only the
first child->parent column pair (the ADR-0019 facts model is single-column).
enrich_fk_violation now gathers all pairs of the matched relationship and
carries them comma-joined in the existing single-column facts slots, so the
headline reads e.g. "no parent row in `Region` has `country, code` = `7, 8`."
instead of naming just `country`.
Single-column behaviour is unchanged (a one-element join is the element
itself). No facts-model or catalog change -- the joined strings flow through
the existing `{parent_column}` / `{value}` placeholders.
Tests: enrichment facts (compound names every pair, single-column
regression) + translate rendering (headline names both columns). 2211 pass
/ 0 fail / 1 ignored. Clippy clean.
claude@clouddev1
5a33f2aeea