fix(ui): stop mislabeling unconverted FX amounts as kr in aggregates and toasts (#1182)

Fixes #1173. invoices.total_sek stays NULL when the Riksbanken rate
fetch fails at creation, and every `total_sek || total` fallback then
treated a raw foreign amount as kronor:

- lib/calendar/utils: new invoiceSekAmount() returns null for
  unconverted non-SEK invoices; period summaries and day totals skip
  them and PeriodSummary exposes unconvertedCount. PaymentSummaryCard
  shows a one-line note when invoices were excluded; CalendarDayView
  renders each invoice in its own currency instead.
- Deadlines page: the overdue attn sum now skips unconverted FX
  invoices and appends "(+N i utlandsk valuta)" instead of adding EUR
  into a kr total.
- Supplier-invoice payment toast formats the amount with the invoice's
  currency (key drops its hardcoded " kr" in both locales).
- AR aging drill-down row labels Betalt with the invoice currency,
  mirroring the outstanding cell.
- BankFileColumnMappingStep: comment pinning why SEK is safe there
  (generic-csv hardcodes it).

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

components/import/BankFileColumnMappingStep.tsx

@@ -408,6 +408,9 @@ export default function BankFileColumnMappingStep({
                             !isNaN(amount) && amount >= 0 ? 'text-success' : 'text-destructive'
                           }`}
                         >
+                          {/* SEK is safe here ONLY because generic-csv hardcodes
+                              currency: 'SEK' (formats/generic-csv.ts). If the
+                              mapper ever gains a currency column, pass it. */}
                           {!isNaN(amount) ? formatCurrency(amount) : amountStr}
                         </TableCell>
                       </TableRow>