Salary module (#245)

* feat: implement salary module with personnummer encryption, salary entries, tax tables, and AGI tracking

- Added personnummer encryption and decryption functions for secure storage.
- Created salary entries handling for journal entries including gross salary, tax withholding, and employer contributions.
- Implemented tax table lookup functionality for calculating tax amounts based on monthly income.
- Developed SQL migration for salary module including tables for payroll configuration, tax rates, employees, salary runs, salary run employees, salary line items, and AGI declarations.
- Established row-level security policies for all new tables to ensure company-scoped access.

* feat: add salary calculation modules for 2026

- Implemented engångsskatt calculation for one-time payments with tax brackets.
- Added löneväxling functionality for salary sacrifice to pension, including employer savings and warnings.
- Created pain.001 generator for salary batch payments in compliance with Swedish banking standards.
- Developed PDF template for payslips, including detailed breakdowns and employer costs.
- Generated seed data for Swedish tax tables for 2026, including SQL insert statements.
- Implemented traktamente calculations for per diem and mileage allowances, adhering to Skatteverket regulations.
- Added seed script for populating tax tables in the database.

* feat: Update meal reduction percentages in traktamente calculation

fix: Remove obsolete seed script for 2026 tax tables

feat: Extend SalaryRunStatus type to include 'corrected' status

feat: Implement KU10 XML generation endpoint for annual employee income statements

feat: Add endpoint for creating corrections to booked salary runs

feat: Implement endpoint for sending payslip PDFs to employees

feat: Create KU10 XML generator for annual reporting

feat: Add salary transaction matcher for auto-linking bank transactions to salary entries

chore: Add database migration for salary correction support

* feat: replace select elements with custom Select component for employment and salary types

* feat: enhance salary calculations with pension entry and avgifter category support

lib/tax/deadline-config.ts

@@ -117,22 +117,27 @@ export const TAX_DEADLINE_CONFIGS: TaxDeadlineConfig[] = [
     },
   },
 
-  // Arbetsgivardeklaration (monthly, AB with employees)
+  // Arbetsgivardeklaration (monthly, any employer with employees — AB or EF)
+  // Per Skatteförfarandelagen: every employer paying salary must file AGI monthly.
+  // Deadline: 12th of following month (17th in Jan/Aug for turnover ≤40 MSEK per agi-filing.md)
   {
     type: 'arbetsgivardeklaration',
     titleTemplate: 'Arbetsgivardeklaration {periodLabel}',
-    description: 'Arbetsgivardeklaration för aktiebolag med anställda',
-    condition: (s) => s.entity_type === 'aktiebolag' && s.pays_salaries,
+    description: 'Arbetsgivardeklaration för arbetsgivare med anställda',
+    condition: (s) => s.pays_salaries,
     priority: 'important',
     linkedReportType: null,
     generateDates: (year) => {
       const instances: DeadlineInstance[] = []
       // Due on the 12th of the following month
+      // Exception: January (for Dec) and August (for Jul) = 17th for ≤40 MSEK turnover
       for (let month = 0; month < 12; month++) {
         const deadlineMonth = (month + 1) % 12
         const deadlineYear = month === 11 ? year + 1 : year
+        // Jan (deadlineMonth=0) and Aug (deadlineMonth=7) get 17th
+        const day = (deadlineMonth === 0 || deadlineMonth === 7) ? 17 : 12
         instances.push({
-          day: 12,
+          day,
           month: deadlineMonth,
           year: deadlineYear,
           period: `${year}-${String(month + 1).padStart(2, '0')}`,