feat(dimensions): PR8 salary — employees.default_dimensions, per-employee cost lines, aggregation re-key (#869)

Employees carry a default dimensions bag and the salary booking puts each
employee's cost on their kostnadsställe/projekt
(dev_docs/dimensions_implementation_plan.md PR8):

- employees.default_dimensions (migration 20260702220000; jsonb DEFAULT
  '{}' + object CHECK)
- salary-entries: the one-line-per-account aggregation is re-keyed to
  account+bag — P&L cost lines (löner incl. line items + base remainder,
  arbetsgivaravgifter, semesteravsättning + dess avgifter, pension, SLP)
  split per employee bag while every balance-sheet/settlement leg (2710,
  1930, 2731, 29xx, 2740, 2514) stays aggregated; liability credits equal
  the sum of the rounded debit buckets so entries balance by construction;
  dimension-less runs book byte-identically to before. Replaces the dead
  SalaryRunEmployee.cost_center/project pair (never wired)
- both book routes (dashboard + v1) read the bag via the employees join —
  read-at-book, so the run review shows exactly what will book
- employee form (new + edit) gets a gated Kostnadsställe/Projekt card;
  run review shows per-employee dims chips; run GET + v1 employee
  routes/schemas + MCP list_employees carry the field
- pre-merge audit: all salary reports (salary-journal, AGI,
  avgifter-basis, vacation-liability) read salary_run_employees — not
  journal lines — and every ledger consumer sums per account, so the
  line split breaks nothing; SIE export + dimension P&L pick the split
  up as intended

8 new engine propagation tests + book-route dims flow test.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/api/v1/companies/[companyId]/employees/[id]/route.ts

@@ -61,13 +61,15 @@ const EmployeeDetail = z.object({
   vaxa_stod_eligible: z.boolean(),
   vaxa_stod_start: z.string().nullable(),
   vaxa_stod_end: z.string().nullable(),
+  // Dimensions PR8: bag applied to the employee's P&L cost lines at booking.
+  default_dimensions: z.record(z.string(), z.string()),
   is_active: z.boolean(),
   created_at: z.string(),
   updated_at: z.string(),
 })
 
 const EMPLOYEE_DETAIL_COLUMNS =
-  'id, first_name, last_name, personnummer, employment_type, employment_start, employment_end, employment_degree, salary_type, monthly_salary, hourly_rate, tax_table_number, tax_column, tax_municipality, is_sidoinkomst, f_skatt_status, clearing_number, bank_account_number, vacation_rule, vacation_days_per_year, semestertillagg_rate, email, phone, address_line1, postal_code, city, vaxa_stod_eligible, vaxa_stod_start, vaxa_stod_end, is_active, created_at, updated_at'
+  'id, first_name, last_name, personnummer, employment_type, employment_start, employment_end, employment_degree, salary_type, monthly_salary, hourly_rate, tax_table_number, tax_column, tax_municipality, is_sidoinkomst, f_skatt_status, clearing_number, bank_account_number, vacation_rule, vacation_days_per_year, semestertillagg_rate, email, phone, address_line1, postal_code, city, vaxa_stod_eligible, vaxa_stod_start, vaxa_stod_end, default_dimensions, is_active, created_at, updated_at'
 
 /**
  * Shape returned by PATCH (success + dry-run preview) and by no-change PATCH.

app/api/v1/companies/[companyId]/employees/route.ts

@@ -429,6 +429,8 @@ export const POST = withApiV1<{ params: Promise<{ companyId: string }> }>(
         vaxa_stod_eligible: body.vaxa_stod_eligible,
         vaxa_stod_start: body.vaxa_stod_start ?? null,
         vaxa_stod_end: body.vaxa_stod_end ?? null,
+        // Dimensions PR8: bag for the employee's P&L cost lines at booking.
+        default_dimensions: body.default_dimensions ?? {},
       })
       .select(EMPLOYEE_RESPONSE_COLUMNS)
       .single()

app/api/v1/companies/[companyId]/salary-runs/[id]/book/route.ts

@@ -154,7 +154,7 @@ export const POST = withApiV1<{ params: Promise<{ companyId: string; id: string
     // 3. Load run + employees + line items for the engine.
     const { data: employees, error: empErr } = await ctx.supabase
       .from('salary_run_employees')
-      .select('*, employee:employees(employment_type), line_items:salary_line_items(*)')
+      .select('*, employee:employees(employment_type, default_dimensions), line_items:salary_line_items(*)')
       .eq('salary_run_id', salaryRunId)
     if (empErr) {
       return v1ErrorResponse(empErr, ctx.log, { requestId: ctx.requestId })
@@ -200,7 +200,7 @@ export const POST = withApiV1<{ params: Promise<{ companyId: string; id: string
     // 4. Engine call. Strict-mode: any throw aborts before status flip.
     type EmpRow = {
       employee_id: string
-      employee: { employment_type: string } | null
+      employee: { employment_type: string; default_dimensions?: Record<string, string> } | null
       gross_salary: number
       tax_withheld: number
       net_salary: number
@@ -242,6 +242,8 @@ export const POST = withApiV1<{ params: Promise<{ companyId: string; id: string
           avgifter_rate: sre.avgifter_rate,
           vacation_accrual: sre.vacation_accrual,
           vacation_accrual_avgifter: sre.vacation_accrual_avgifter,
+          // Dimensions PR8: read-at-book from the employee row.
+          default_dimensions: sre.employee?.default_dimensions ?? undefined,
           line_items: (sre.line_items || []).map((li) => ({
             item_type: li.item_type,
             amount: li.amount,