fix: address user feedback — RC preview, bank sync lookback, CSV import robustness (#233)

Three confirmed issues from user feedback:

1. Reverse charge preview now uses per-item VAT rates and correct accounts
   (2645/2647, 2614/2624/2634) instead of hardcoded 25%/2614
2. Bank sync uses 90-day lookback on first sync (when last_synced_at is null)
   instead of hardcoded 7 days for all syncs
3. Bank file import improvements:
   - Shared date normalizer supporting DD.MM.YYYY, DD/MM/YYYY, YYYYMMDD
   - Silent row skips now reported with reason in issues[]
   - Decimal separator mismatch detection in generic CSV
   - Swedish error message with format diagnostics on detection failure
   - Date format selector in column mapping UI

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

components/import/BankFileColumnMappingStep.tsx

@@ -44,6 +44,7 @@ export default function BankFileColumnMappingStep({
   const [balanceCol, setBalanceCol] = useState<number>(-1)
   const [delimiter, setDelimiter] = useState<string>(',')
   const [decimalSep, setDecimalSep] = useState<',' | '.'>(',')
+  const [dateFormat, setDateFormat] = useState<string>('YYYY-MM-DD')
 
   const isValid = dateCol >= 0 && descCol >= 0 && amountCol >= 0
 
@@ -58,7 +59,7 @@ export default function BankFileColumnMappingStep({
       delimiter,
       decimal_separator: decimalSep,
       skip_rows: 1, // Skip header
-      date_format: 'YYYY-MM-DD',
+      date_format: dateFormat,
     }
     onConfirm(mapping)
   }
@@ -78,8 +79,8 @@ export default function BankFileColumnMappingStep({
           </CardDescription>
         </CardHeader>
         <CardContent className="space-y-6">
-          {/* Delimiter and decimal settings */}
-          <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
+          {/* Delimiter, decimal, and date format settings */}
+          <div className="grid grid-cols-1 sm:grid-cols-3 gap-4">
             <div className="space-y-2">
               <Label>Avgränsare</Label>
               <Select value={delimiter} onValueChange={(v) => { if (v) setDelimiter(v) }}>
@@ -105,6 +106,20 @@ export default function BankFileColumnMappingStep({
                 </SelectContent>
               </Select>
             </div>
+            <div className="space-y-2">
+              <Label>Datumformat</Label>
+              <Select value={dateFormat} onValueChange={(v) => { if (v) setDateFormat(v) }}>
+                <SelectTrigger>
+                  <SelectValue />
+                </SelectTrigger>
+                <SelectContent>
+                  <SelectItem value="YYYY-MM-DD">YYYY-MM-DD</SelectItem>
+                  <SelectItem value="DD.MM.YYYY">DD.MM.YYYY</SelectItem>
+                  <SelectItem value="DD/MM/YYYY">DD/MM/YYYY</SelectItem>
+                  <SelectItem value="YYYYMMDD">YYYYMMDD</SelectItem>
+                </SelectContent>
+              </Select>
+            </div>
           </div>
 
           {/* Required column mappings */}

components/suppliers/SupplierInvoiceReviewContent.tsx

@@ -40,12 +40,19 @@ interface JournalPreviewLine {
   credit: number
 }
 
+function getOutputVatAccount(rate: number): string {
+  if (rate === 0.12) return '2624'
+  if (rate === 0.06) return '2634'
+  return '2614'
+}
+
 function buildJournalPreview(
   items: ReviewLineItem[],
   subtotal: number,
   totalVat: number,
   total: number,
   reverseCharge: boolean,
+  supplierType?: string,
 ): JournalPreviewLine[] {
   const lines: JournalPreviewLine[] = []
 
@@ -67,21 +74,35 @@ function buildJournalPreview(
   }
 
   if (reverseCharge) {
-    // EU reverse charge: fiktiv moms
-    const vatRate = 0.25
-    const fiktivVat = Math.round(subtotal * vatRate * 100) / 100
-    lines.push({
-      account_number: '2645',
-      description: 'Beräknad ingående moms',
-      debit: fiktivVat,
-      credit: 0,
-    })
-    lines.push({
-      account_number: '2614',
-      description: 'Utgående moms omvänd',
-      debit: 0,
-      credit: fiktivVat,
-    })
+    // Reverse charge: fiktiv moms per VAT rate (matches engine groupVatByRate logic)
+    const isDomesticRC = supplierType === 'swedish_business'
+    const inputAccount = isDomesticRC ? '2647' : '2645'
+
+    const vatByRate = new Map<number, number>()
+    for (const item of items) {
+      if (item.vat_rate > 0) {
+        const current = vatByRate.get(item.vat_rate) || 0
+        vatByRate.set(item.vat_rate, current + Math.round(item.amount * 100) / 100)
+      }
+    }
+
+    for (const [rate, netAmount] of vatByRate) {
+      const fiktivVat = Math.round(netAmount * rate * 100) / 100
+      const outputAccount = getOutputVatAccount(rate)
+      lines.push({
+        account_number: inputAccount,
+        description: inputAccount,
+        debit: fiktivVat,
+        credit: 0,
+      })
+      lines.push({
+        account_number: outputAccount,
+        description: outputAccount,
+        debit: 0,
+        credit: fiktivVat,
+      })
+    }
+
     // Credit: 2440 at subtotal (no real VAT for reverse charge)
     lines.push({
       account_number: '2440',
@@ -113,8 +134,11 @@ function buildJournalPreview(
 const ACCOUNT_LABELS: Record<string, string> = {
   '2440': 'Leverantörsskulder',
   '2641': 'Ingående moms',
-  '2645': 'Beräknad ingående moms',
-  '2614': 'Utg. moms omvänd skattskyldighet',
+  '2645': 'Beräknad ing. moms förvärv utlandet',
+  '2647': 'Beräknad ing. moms omvänd i Sverige',
+  '2614': 'Utg. moms omvänd 25%',
+  '2624': 'Utg. moms omvänd 12%',
+  '2634': 'Utg. moms omvänd 6%',
 }
 
 export function SupplierInvoiceReviewContent({
@@ -132,7 +156,7 @@ export function SupplierInvoiceReviewContent({
   totalVat,
   total,
 }: SupplierInvoiceReviewContentProps) {
-  const journalLines = buildJournalPreview(items, subtotal, totalVat, total, reverseCharge)
+  const journalLines = buildJournalPreview(items, subtotal, totalVat, total, reverseCharge, supplier.supplier_type)
   const totalDebit = journalLines.reduce((sum, l) => sum + l.debit, 0)
   const totalCredit = journalLines.reduce((sum, l) => sum + l.credit, 0)