Match a bank statement against unpaid invoices

Parses one or more uploaded bank-statement files (CSV or Excel) into transactions, keeps incoming credits, and matches them against the user's unpaid (non-quote) invoices. Matching is reference-first: an invoice reference (hash, e.g. NA001) or an exact-total amount with a strong client-name match is auto-applied (invoice marked paid + a payment recorded); a credit below the total that strongly identifies an invoice records a partial payment without marking it paid. Lower-confidence amount-only matches are returned as suggestions and never applied. Re-importing the same statement is idempotent (payments are de-duplicated by amount + date). When a non-CHF invoice is marked paid, its CHF exchange rate is stored.