Salary module improvements (#250)

* 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

* feat: enhance employee management with salary type, tax status, and validation improvements

* feat: Implement AGI submission flow to Skatteverket

- Added AGI submission route to handle the submission process.
- Created AGI client for interacting with Skatteverket's API.
- Introduced AGI mappers to convert salary run data into the required AGI JSON payload format.
- Enhanced API client to support custom base URLs for Skatteverket API requests.
- Added types for AGI submission payload and validation results.
- Implemented tests for AGI mappers to ensure correct payload structure and data handling.

* feat: enhance salary module with Skatteverket integration and update dashboard navigation

* Update app/api/salary/runs/[id]/agi/submit/route.ts

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

* Update app/api/salary/runs/[id]/approve/route.ts

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

* feat: integrate write permission check and remove Skatteverket extension

---------

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

app/api/salary/employees/[id]/route.ts

@@ -57,10 +57,10 @@ export async function PATCH(
   if (!validation.success) return validation.response
   const body = validation.data
 
-  // Check employee exists
+  // Load existing employee for merged validation
   const { data: existing, error: fetchError } = await supabase
     .from('employees')
-    .select('id')
+    .select('*')
     .eq('id', id)
     .eq('company_id', companyId)
     .single()
@@ -69,6 +69,23 @@ export async function PATCH(
     return NextResponse.json({ error: 'Anställd hittades inte' }, { status: 404 })
   }
 
+  // Merged validation: combine existing + updates to check full integrity
+  const merged = { ...existing, ...body }
+  const mergedErrors: string[] = []
+
+  if (merged.salary_type === 'monthly' && (!merged.monthly_salary || merged.monthly_salary <= 0)) {
+    mergedErrors.push('Månadslön krävs och måste vara större än 0 för månadslöneform')
+  }
+  if (merged.salary_type === 'hourly' && (!merged.hourly_rate || merged.hourly_rate <= 0)) {
+    mergedErrors.push('Timlön krävs och måste vara större än 0 för timlöneform')
+  }
+  if (merged.f_skatt_status === 'a_skatt' && !merged.is_sidoinkomst && !merged.tax_table_number) {
+    mergedErrors.push('Skattetabell krävs för A-skatt anställda')
+  }
+  if (mergedErrors.length > 0) {
+    return NextResponse.json({ error: mergedErrors.join('. ') }, { status: 400 })
+  }
+
   // Build update object
   const updates: Record<string, unknown> = { ...body }