Import a CSV of expenditure items into the claim.

Admin-only. Accepts a multipart upload with file (the CSV), mode (append | replace), and column_mapping (JSON object mapping target field names to CSV header names — see _CSV_IMPORT_TARGET_FIELDS).

• append: keeps every existing item; creates a new import record and inserts the parsed rows alongside.
• replace: soft-deletes every active item on the claim across every prior import (Xero/QBO included) before inserting the CSV rows. The caller signed off on this scope. Re-running Xero/QBO will un-soft-delete matching rows from those sources, but any prior manual category edits on the wiped rows are lost.

Rows whose eligibility cell is a valid value (r_and_d/ non_eligible) are inserted with manual_override=True. Rows with blank/invalid eligibility are inserted uncategorised for the user to categorise manually on the categorised page.

Activity-name lookup is by exact name within the claim's projects. Misses are surfaced in skip_reasons and the row is inserted with activity_id = NULL.

Auth is intentionally a pair of dependencies: get_admin_user checks the real session owner (so impersonation can't elevate), and get_released_editable_salary_visible_claim_for_user checks claim access and editability on the active identity. Don't collapse them.