Import ING and Kontist statements behind a reviewed column mapping

CSV import is now mapping-driven: N26, ING (metadata preamble, Windows-1252,
German decimals) and Kontist exports are recognized locally, and any other
layout can have its columns proposed by the configured model from a sample in
which letters are replaced by x and digits by 0. Proposals are untrusted: every
column must name a supplied header, money must come from one signed column or
one debit/credit pair, and formats must be from a closed list.

Uploading no longer imports. /api/import is replaced by prepare/confirm/cancel:
prepare parses, deduplicates and previews the exact facts, and only confirming
at the reviewed revision writes them. ING and AI-mapped facts carry no
transaction reference, because repeating SEPA mandate references must never
become a transaction identity.

internal/banking/import.go

@@ -42,6 +42,12 @@ func sourceLabel(source string) string {
 		return "bank-synced"
 	case "n26_csv":
 		return "CSV"
+	case "ing_csv":
+		return "ING CSV"
+	case "kontist_csv":
+		return "Kontist CSV"
+	case "csv":
+		return "mapped CSV"
 	default:
 		return "source " + strconv.Quote(source)
 	}