fix: Swedish VAT compliance — representation, domestic RC, full 26xx mapping, SIE (#206)

* 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>

* fix: Swedish VAT compliance — representation VAT, domestic RC, full BAS 26xx mapping, SIE encoding

- Representation expenses now default to reduced_12 VAT (ML 13 kap 24-25 §§);
  income tax deduction was abolished 2017 but VAT deduction at 12% remains
- Domestic reverse charge (byggtjänster etc.) uses 2647 instead of 2645,
  with distinct line descriptions for Swedish vs EU/non-EU RC
- VAT declaration maps all BAS 26xx variant accounts (egna uttag 2612/2622/2632,
  uthyrning 2613/2623/2633, VMB 2616/2626/2636, import 2615/2625/2635,
  domestic RC 2647, frivillig skattskyldighet 2642) and revenue variants
  (3108/3105/3004/3100) to correct momsdeklaration rutor
- SIE parser: remove unreliable #FORMAT PC8 encoding detection (most software
  exports UTF-8 with PC8 header), parse #FLAGGA for import-already-done warning,
  default SIE type to 1 when absent, fix RTRANS/BTRANS documentation
- SIE export: add #RAR -1 (previous fiscal year), fix UB = IB + movements
- Error messages: add pattern matching for locked period trigger errors

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

* fix: address Greptile review — update ruta49 JSDoc, use null sentinel in error map

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

---------

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

lib/vat/moms-box-mapping.ts

@@ -42,7 +42,7 @@ export type MomsBox =
   | '61'  // Importmoms 12%
   | '62'  // Importmoms 6%
 
-/** Map BAS revenue account to momsdeklaration box */
+/** Map BAS account to momsdeklaration box */
 export const ACCOUNT_TO_BOX: Record<string, MomsBox> = {
   // Domestic revenue (taxable) → Box 05
   '3001': '05',  // Försäljning varor/tjänster 25%
@@ -66,14 +66,43 @@ export const ACCOUNT_TO_BOX: Record<string, MomsBox> = {
   // Non-EU services → Box 40
   '3305': '40',  // Försäljning tjänster export utanför EU
 
-  // Output VAT → Boxes 10, 11, 12
-  '2611': '10',  // Utgående moms 25%
-  '2621': '11',  // Utgående moms 12%
-  '2631': '12',  // Utgående moms 6%
+  // VAT-exempt sales → Box 42
+  '3004': '42',  // Momsfri försäljning (AB)
+  '3100': '42',  // Momsfria intäkter (EF)
+
+  // Output VAT 25% → Box 10
+  '2611': '10',  // Försäljning inom Sverige
+  '2612': '10',  // Egna uttag
+  '2613': '10',  // Uthyrning (frivillig skattskyldighet)
+  '2616': '10',  // Vinstmarginalbeskattning
+  // Output VAT 12% → Box 11
+  '2621': '11',
+  '2622': '11',  // Egna uttag
+  '2623': '11',  // Uthyrning
+  '2626': '11',  // VMB
+  // Output VAT 6% → Box 12
+  '2631': '12',
+  '2632': '12',  // Egna uttag
+  '2633': '12',  // Uthyrning
+  '2636': '12',  // VMB
+
+  // Reverse charge output VAT → Boxes 30, 31, 32
+  '2614': '30',
+  '2624': '31',
+  '2634': '32',
+
+  // Import VAT (since 2015, via momsdeklaration) → Boxes 60, 61, 62
+  '2615': '60',  // Import 25%
+  '2625': '61',  // Import 12%
+  '2635': '62',  // Import 6%
 
   // Input VAT → Box 48
-  '2641': '48',  // Ingående moms
-  '2645': '48',  // Beräknad ingående moms (EU förvärv)
+  '2641': '48',  // Debiterad ingående moms
+  '2642': '48',  // Frivillig skattskyldighet
+  '2645': '48',  // Beräknad ingående moms (EU/non-EU förvärv)
+  '2646': '48',  // Uthyrning
+  '2647': '48',  // Omvänd skattskyldighet i Sverige
+  '2649': '48',  // Blandad verksamhet
 }
 
 /** Swedish labels for each momsdeklaration box */