Add evidence files to a back work bookkeeping program

Requires firm owner/admin accounting authority. Accepts either multipart uploads (up to 50 CSV/XLSX/ZIP files, 50 MB) under the files field, or JSON with workspacePaths and/or evidenceIds (1–50 total) to load existing workspace files or chat attachments into program intake. Saves each file best-effort with collision-safe names, safely expands ZIP archives, always rescans files saved before any later failure, and returns both per-file outcomes and the refreshed account-by-month scan. ZIP containers remain stored for replay but are omitted from visible evidence counts. Clean scans do not auto-start pre-flight; call Begin Import when the firm is done adding files.