Delete features (#218)

* 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.

lib/auth/require-write.ts

@@ -0,0 +1,63 @@
+import { NextResponse } from 'next/server'
+import type { SupabaseClient } from '@supabase/supabase-js'
+import { getActiveCompanyId } from '@/lib/company/context'
+
+/**
+ * Write-permission guard for API routes.
+ *
+ * Looks up the caller's role in the currently active company. Returns a
+ * 403 JSON response if the role is 'viewer' (or if the user has no role
+ * in any resolvable company). Any other role (owner / admin / member)
+ * passes.
+ *
+ * Meant to be called AFTER `requireAuth()` in every API route that
+ * mutates tenant data (POST / PATCH / PUT / DELETE). Read-only POSTs
+ * that only generate PDFs or run utility lookups (e.g. VAT validation)
+ * should skip this check.
+ *
+ * This is the application-layer half of the defense-in-depth story; the
+ * RLS helper `public.current_user_can_write()` is the database half.
+ * Having both means a viewer who bypasses the JS UI and calls the API
+ * directly still gets a clean 403, and even if someone forgets to add
+ * this guard to a new route, the RLS policy blocks the write at the
+ * database layer.
+ */
+type WritePermissionResult =
+  | { ok: true }
+  | { ok: false; response: NextResponse }
+
+export async function requireWritePermission(
+  supabase: SupabaseClient,
+  userId: string,
+): Promise<WritePermissionResult> {
+  const companyId = await getActiveCompanyId(supabase, userId)
+
+  if (!companyId) {
+    return {
+      ok: false,
+      response: NextResponse.json(
+        { error: 'Inget aktivt företag.' },
+        { status: 403 },
+      ),
+    }
+  }
+
+  const { data: membership } = await supabase
+    .from('company_members')
+    .select('role')
+    .eq('company_id', companyId)
+    .eq('user_id', userId)
+    .maybeSingle()
+
+  if (!membership || membership.role === 'viewer') {
+    return {
+      ok: false,
+      response: NextResponse.json(
+        { error: 'Du har endast läsbehörighet i detta företag.' },
+        { status: 403 },
+      ),
+    }
+  }
+
+  return { ok: true }
+}