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

lib/api/schemas.ts

@@ -305,7 +305,7 @@ export const CreateJournalEntrySchema = z.object({
   description: z.string().min(1, 'Description is required'),
   source_type: JournalEntrySourceTypeSchema.default('manual'),
   source_id: z.string().optional(),
-  voucher_series: z.string().optional(),
+  voucher_series: z.string().regex(/^[A-Z]$/, 'Verifikationsserie måste vara en bokstav A–Z').optional(),
   lines: z.array(CreateJournalEntryLineSchema).min(2, 'At least two lines are required for double-entry'),
 })
 
@@ -384,6 +384,8 @@ export const UpdateSettingsSchema = z.object({
   // Bookkeeping lock
   bookkeeping_locked_through: z.string().regex(/^\d{4}-\d{2}-\d{2}$/, 'Ogiltigt datumformat (YYYY-MM-DD)').nullable().optional(),
   auto_lock_period_days: z.number().int().positive().nullable().optional(),
+  // Voucher series
+  default_voucher_series: z.string().regex(/^[A-Z]$/, 'Verifikationsserie måste vara en bokstav A–Z').optional(),
   // Invoice PDF settings
   ore_rounding: z.boolean().optional(),
   invoice_show_ocr: z.boolean().optional(),
@@ -584,7 +586,7 @@ export const PendingOperationsQuerySchema = z.object({
 
 export const VoucherGapQuerySchema = z.object({
   fiscal_period_id: uuid,
-  voucher_series: z.string().optional(),
+  voucher_series: z.string().regex(/^[A-Z]$/, 'Verifikationsserie måste vara en bokstav A–Z').optional(),
 })
 
 export const SaveGapExplanationSchema = z.object({