Create Fields Batch

Create many custom columns (contacts or companies) in ONE request.

Backed by a single DB transaction with ONE view rebuild for the whole batch — the efficient path for setting up a list with dozens of columns at once. The single-column POST /fields is unchanged; this is purely additive.

Validation is fail-fast: data_types, duplicate titles, and every enrichment block are checked BEFORE any column is created, so a bad request creates nothing. Column creation itself is atomic (all columns or none).

Per-column enrichment blocks are applied AFTER the columns commit; if a companion enrichment config fails for one column, that column still exists and its results[] entry reports ok=false with the error — the rest of the batch is unaffected (mirrors the single endpoint's column-then-config ordering, but per-field instead of failing the whole request).