Voucher series switcher (#219)

* Implement company and account deletion features

- Add event types for company and account deletion to CoreEvent.
- Enhance Supabase middleware to handle company context resolution and cookie management for archived companies.
- Create API routes for deleting accounts and companies, including necessary validations and event emissions.
- Implement tests for account and company deletion endpoints to ensure proper functionality and error handling.
- Add retention notice component to inform users about bookkeeping data retention during destructive actions.
- Create database migrations to support soft deletion of companies and anonymization of user accounts, ensuring compliance with retention laws.

* feat: enhance account deletion process and update user notifications

* Add service client for onboarding completion check and update escape hatch visibility

* Enhance invite flow and email handling for company members

* Refactor company context and RLS policies for active company isolation

- Update `switchCompany` to remove unnecessary revalidation as client handles navigation.
- Revise `getActiveCompanyId` to prioritize `user_preferences` and validate against non-archived memberships.
- Modify `setActiveCompany` to ensure `user_preferences` is the authoritative source while maintaining cookie compatibility.
- Enhance middleware to resolve active company using `user_preferences` and fallback to first non-archived membership.
- Introduce new API route `/api/company/current` to fetch the active company ID for cross-tab synchronization.
- Implement `CompanyTabSync` component for real-time active company enforcement across tabs.
- Create migration for RLS policies to enforce single-active-company isolation using `current_active_company_id()`.

* feat: implement viewer role enforcement for write permissions

- Added `useCanWrite` hook to determine if the current user has write permissions based on their role in the active company.
- Updated various components (JournalEntryForm, CustomerForm, DeadlineForm, etc.) to disable write actions and show a lock icon with a tooltip for users without write permissions.
- Introduced `requireWritePermission` function to enforce write permissions at the API level, returning a 403 response for viewers.
- Created tests to verify the behavior of the viewer role and write permissions.
- Added database migration to enforce read-only access for viewers at the database level.

* Add default voucher series configuration for manual journal entries

app/(dashboard)/settings/bookkeeping/page.tsx

@@ -10,6 +10,8 @@ import { Label } from '@/components/ui/label'
 import { ExternalLink } from 'lucide-react'
 import type { CompanySettings } from '@/types'
 
+const SERIES_OPTIONS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('')
+
 export default function BookkeepingSettingsPage() {
   const { settings, isLoading, updateSettings } = useSettings()
 
@@ -19,11 +21,13 @@ export default function BookkeepingSettingsPage() {
     const autoLockValue = formData.get('auto_lock_period_days') as string
     const lockedThrough = (formData.get('bookkeeping_locked_through') as string) || null
     const accountingMethod = (formData.get('accounting_method') as string) || 'accrual'
+    const defaultVoucherSeries = (formData.get('default_voucher_series') as string) || 'A'
 
     const updates: Record<string, unknown> = {
       bookkeeping_locked_through: lockedThrough,
       auto_lock_period_days: autoLockValue === 'none' ? null : parseInt(autoLockValue),
       accounting_method: accountingMethod,
+      default_voucher_series: defaultVoucherSeries,
     }
     return {
       updates,
@@ -60,15 +64,40 @@ export default function BookkeepingSettingsPage() {
           </div>
         </section>
 
+        {/* Default voucher series */}
+        <div className="border-t border-border/8 pt-8">
+          <section className="space-y-4">
+            <h2 className="text-sm font-medium uppercase tracking-wider text-muted-foreground">
+              Standardserie för verifikationer
+            </h2>
+            <div className="space-y-2">
+              <Label htmlFor="default_voucher_series">Serie</Label>
+              <select
+                id="default_voucher_series"
+                name="default_voucher_series"
+                defaultValue={settings.default_voucher_series || 'A'}
+                className="flex h-10 w-16 rounded-md border border-input bg-background px-3 py-2 text-sm font-mono ring-offset-background focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2"
+              >
+                {SERIES_OPTIONS.map((letter) => (
+                  <option key={letter} value={letter}>{letter}</option>
+                ))}
+              </select>
+              <p className="text-xs text-muted-foreground">
+                Vilken serie som förväljs vid manuell bokföring. Kan ändras per verifikation.
+              </p>
+            </div>
+          </section>
+        </div>
+
         {/* Period locking */}
         <div className="border-t border-border/8 pt-8">
           <PeriodLockingSettings settings={settings} />
         </div>
       </SettingsFormWrapper>
 
-      {/* Voucher series — read-only, no form submit needed */}
+      {/* Voucher series — read-only display */}
       <div className="border-t border-border/8 pt-8">
-        <VoucherSeriesManager />
+        <VoucherSeriesManager defaultSeries={settings.default_voucher_series || 'A'} />
       </div>
 
       {/* Cross-links */}