Add company-scoped brand and company settings API.

brand now carries a NOT NULL company_id (unique per (company_id, name))
with brand.list/upsert/delete backed by resolveCompanyAccess. Adds
companysetting key-value store (list/get/set/delete, frontend flag).

src/sql/purge.js

@@ -2,6 +2,7 @@
 export const TABLES = [
   'companyuser',
   'syncpos',
+  'companysetting',
   'numbers',
   'manifestarticle',
   'manifest',