feat: INK2 declaration improvements, invoice delivery date & Swedish compliance skills (#204)

* feat: add INK2 declaration improvements, invoice delivery date, and Swedish compliance skills

Expand INK2 engine with full INK2S/INK2R support and improved SRU generation.
Add delivery_date field to invoices and corresponding PDF/migration support.
Add Claude skills for Swedish asset accounting, invoice compliance, SIE import/export, SRU filing, and tax planning.

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

* fix: address PR review — map BAS 4500–4899, strip CRLF in SRU, document P3

- Map BAS accounts 4500–4599 (legoarbeten), 4700–4899 (diverse
  varuinköpskostnader) to SRU 7512 so they are not silently dropped
  from INK2R declarations
- Strip \r\n in sanitizeString to prevent CRLF injection in SRU fields
- Document P3 period suffix limitation for brutet räkenskapsår

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

* fix: correct BAS 4500-4599, 4700-4899 mapping from 7512 to 7511

Per the official BAS-to-SRU mapping, these account ranges are cost of
goods (legoarbeten, inkurans, svinn) and belong under 7511 (Råvaror
och förnödenheter), not 7512 (Handelsvaror). 7512 remains 4600-4699.

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

---------

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

app/api/invoices/preview-pdf/route.ts

@@ -24,7 +24,7 @@ export async function POST(request: Request) {
   const companyId = await requireCompanyId(supabase, user.id)
 
   const body = await request.json()
-  const { customer_id, invoice_date, due_date, currency, items, your_reference, our_reference, notes, document_type } = body
+  const { customer_id, invoice_date, due_date, delivery_date, currency, items, your_reference, our_reference, notes, document_type } = body
 
   if (!customer_id || !items || items.length === 0) {
     return NextResponse.json({ error: 'Kunduppgifter och rader krävs' }, { status: 400 })
@@ -93,6 +93,7 @@ export async function POST(request: Request) {
     invoice_number: 'FÖRHANDSGRANSKNING',
     invoice_date: invoice_date || new Date().toISOString().split('T')[0],
     due_date: due_date || new Date().toISOString().split('T')[0],
+    delivery_date: delivery_date || null,
     status: 'draft',
     currency: currency || 'SEK',
     exchange_rate: null,

app/api/invoices/route.ts

@@ -188,6 +188,7 @@ export async function POST(request: Request) {
       invoice_number: invoiceNumber,
       invoice_date: invoiceInput.invoice_date,
       due_date: invoiceInput.due_date,
+      delivery_date: invoiceInput.delivery_date ?? null,
       currency: invoiceInput.currency,
       exchange_rate: exchangeRate,
       exchange_rate_date: exchangeRateDate,
@@ -312,6 +313,7 @@ async function createCreditNote(
       invoice_number: creditNoteNumber,
       invoice_date: new Date().toISOString().split('T')[0],
       due_date: new Date().toISOString().split('T')[0],
+      delivery_date: originalInvoice.delivery_date ?? null,
       currency: originalInvoice.currency,
       exchange_rate: originalInvoice.exchange_rate,
       exchange_rate_date: originalInvoice.exchange_rate_date,

app/api/reports/ink2/route.ts

@@ -2,11 +2,11 @@ import { createClient } from '@/lib/supabase/server'
 import { NextResponse } from 'next/server'
 import { generateINK2Declaration } from '@/lib/reports/ink2/ink2-engine'
 import {
-  generateSRUFile,
-  sruFileToString,
-  getSRUFilename,
+  generateSRUSubmission,
+  getZipFilename,
 } from '@/lib/reports/ink2/sru-generator'
 import { requireCompanyId } from '@/lib/company/context'
+import JSZip from 'jszip'
 
 /**
  * GET /api/reports/ink2
@@ -15,7 +15,7 @@ import { requireCompanyId } from '@/lib/company/context'
  *
  * Query parameters:
  * - period_id: Fiscal period ID (required)
- * - format: 'json' (default) or 'sru' for SRU file download
+ * - format: 'json' (default) or 'sru' for SRU file download (ZIP with INFO.SRU + BLANKETTER.SRU)
  */
 export async function GET(request: Request) {
   const supabase = await createClient()
@@ -42,14 +42,24 @@ export async function GET(request: Request) {
     const declaration = await generateINK2Declaration(supabase, companyId, periodId)
 
     if (format === 'sru') {
-      const sruFile = generateSRUFile(declaration)
-      const sruContent = sruFileToString(sruFile)
-      const filename = getSRUFilename(declaration)
+      const submission = generateSRUSubmission(declaration)
 
-      return new NextResponse(sruContent, {
+      // Encode both files as ISO 8859-1 (Latin-1) — required by Skatteverket
+      const infoBytes = encodeISO88591(submission.infoSru)
+      const blanketterBytes = encodeISO88591(submission.blanketterSru)
+
+      // Create ZIP with both files
+      const zip = new JSZip()
+      zip.file('INFO.SRU', infoBytes)
+      zip.file('BLANKETTER.SRU', blanketterBytes)
+
+      const zipArrayBuffer = await zip.generateAsync({ type: 'arraybuffer' })
+      const filename = getZipFilename(declaration)
+
+      return new NextResponse(zipArrayBuffer, {
         status: 200,
         headers: {
-          'Content-Type': 'text/plain; charset=utf-8',
+          'Content-Type': 'application/zip',
           'Content-Disposition': `attachment; filename="${filename}"`,
         },
       })
@@ -64,3 +74,16 @@ export async function GET(request: Request) {
     )
   }
 }
+
+/**
+ * Encode a string as ISO 8859-1 (Latin-1) bytes.
+ * Characters outside the Latin-1 range are replaced with '?'.
+ */
+function encodeISO88591(str: string): Uint8Array {
+  const bytes = new Uint8Array(str.length)
+  for (let i = 0; i < str.length; i++) {
+    const code = str.charCodeAt(i)
+    bytes[i] = code <= 0xFF ? code : 0x3F // '?' for unmappable chars
+  }
+  return bytes
+}