feat(rbac): GDPR export becomes a toggleable clients.gdpr_export permission

Previously the GDPR export trigger + download routes were gated by
admin.manage_settings, so sales roles couldn't run a client data export.
Per request, make it a dedicated, toggleable permission that's on by
default for sales-capable roles and hides the button when withheld.

- New RolePermissions leaf clients.gdpr_export (+ PERMISSION_CATALOG entry);
  strict type forces every role map + fixture to declare it.
- Granted true for super_admin / director / sales_manager / sales_agent;
  false for viewer / residential_partner.
- GDPR export POST (trigger) and [exportId] GET (download) re-gated from
  admin.manage_settings -> clients.gdpr_export.
- GdprExportButton visibility now keys off clients.gdpr_export, so toggling
  it off per-user hides the function entirely.
- Migration 0098 backfills the key onto existing role rows (idempotent).

Verified end-to-end as a Sales user: trigger (202) -> worker build (ready)
-> list (200) -> download (200). 1664 vitest pass; tsc + eslint clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/auth/permissions.ts

@@ -21,7 +21,7 @@ export type PermissionAction<R extends PermissionResource> = keyof RolePermissio
  * (audit finding L23).
  */
 export const PERMISSION_CATALOG = {
-  clients: ['view', 'create', 'edit', 'delete', 'merge', 'export'],
+  clients: ['view', 'create', 'edit', 'delete', 'merge', 'export', 'gdpr_export'],
   interests: [
     'view',
     'create',