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/import/__tests__/sie-import.test.ts

@@ -8,6 +8,7 @@ function makeParsedFile(overrides?: Partial<ParsedSIEFile>): ParsedSIEFile {
   return {
     header: {
       sieType: 4,
+      flagga: 0,
       program: 'TestProg',
       programVersion: '1.0',
       generatedDate: '2024-01-01',

lib/import/__tests__/sie-parser.test.ts

@@ -440,16 +440,19 @@ describe('validateSIEFile', () => {
 // --- Fix 2: Windows-1252 encoding detection and decoding ---
 
 describe('detectEncoding — #FORMAT PC8 detection', () => {
-  it('returns cp437 when #FORMAT PC8 is present in the first 500 bytes', () => {
-    const text = '#FLAGGA 0\n#FORMAT PC8\n#SIETYP 4\n'
-    const encoder = new TextEncoder()
+  it('ignores #FORMAT PC8 and detects UTF-8 from byte patterns', () => {
+    // #FORMAT PC8 is unreliable — most cloud software (Fortnox, Bokio etc.)
+    // exports UTF-8 but still declares #FORMAT PC8.
+    // UTF-8 encoded: "Företagskonto" → 0xC3 0xB6 for ö
+    const text = '#FLAGGA 0\n#FORMAT PC8\n#FNAMN "Företagskonto"\n'
+    const encoder = new TextEncoder() // TextEncoder outputs UTF-8
     const buf = encoder.encode(text)
     const encoding = detectEncoding(buf.buffer)
-    expect(encoding).toBe('cp437')
+    expect(encoding).toBe('utf8')
   })
 
-  it('returns cp437 even when Win-1252 bytes follow #FORMAT PC8', () => {
-    // #FORMAT PC8 header should take priority over any byte analysis
+  it('detects Win-1252 when actual byte values are in Win-1252 range', () => {
+    // Win-1252 bytes for Swedish chars: ö=0xF6, ä=0xE4, å=0xE5
     const prefix = new TextEncoder().encode('#FORMAT PC8\n#FNAMN F')
     const buf = new Uint8Array(prefix.length + 3)
     buf.set(prefix)
@@ -457,7 +460,15 @@ describe('detectEncoding — #FORMAT PC8 detection', () => {
     buf[prefix.length + 1] = 0xe4 // ä in Win-1252
     buf[prefix.length + 2] = 0xe5 // å in Win-1252
     const encoding = detectEncoding(buf.buffer)
-    expect(encoding).toBe('cp437')
+    expect(encoding).toBe('windows1252')
+  })
+
+  it('returns utf8 for pure ASCII files (no high bytes)', () => {
+    const text = '#FLAGGA 0\n#FORMAT PC8\n#SIETYP 4\n'
+    const encoder = new TextEncoder()
+    const buf = encoder.encode(text)
+    const encoding = detectEncoding(buf.buffer)
+    expect(encoding).toBe('utf8')
   })
 })